A MONTI-ILY IRAPIO

A MONTI-ILY OIiE1 or

IRAPIO AND ÂLLII7 MÂ1NT!NÂNE

PER COPY

15 CENTS

Way down east .. .

(see page 195)

AUGUST 1932

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THIS VOLUME SHOULD SELL FOR $10.00 COMPARED WITH OTHERS ON THE MARKET - BUT -

IT SELLS FOR ONLY $5.00 Volume II is the companion Manual to Volume I. Volume II contains all new information,

none of which appeared in Volume I and mast of which will not be found in any other Manual published today.

If you own a copy of Volume I, you will want. Volume II immediately. Volume II shows diagrams of sets produced since the publication of Volume I and the two Manuals together represent a complete diagrammatic history of radio receivers since the beginning.

Volume II fulfills the demands made by Service Men for full electrical values of resistors and condensers. For instance, THE ELECTRICAL VALUES OF ATWATER KENT RECEIVERS ARE GIVEN IN COMPLETE DETAIL.

Volume II has been prepared on the basis of the results of a comprehensive survey, made to determine exactly what Service Men want and need in a Manual. It includes wiring diagrams, chassis layouts, socket layouts, alignment data, peak frequencies, location of trimmers, color coding, electrical continuity of units sealed in cans, special notes, circuit peculiarities, voltage data and other important information. Special attention has been given to auto -radio, automatic record changers, superheterodyne converters-everything necessary to the successful operation of a service business.

SPECIAL-More Than 50 Pages of Point -to -Point Resistance Data Buy it from Your Dealer. Sold with a Money -Back

Alabama Auto Elec. Service Co --Montgomery

Australia McGill's Melbourne

California Radio Mtg. Supply Co Los Angeles Radio Supply Co Los Angeles Offenbach an Francisco Warner Bros San Francisco

Canada T. Eaton Co Winnipeg Edwin J. Galloway..Vancouver, B. C.

District of Columbia Star Radio Co Washington

Connecticut S. S. Kresge New Haven S. S, Kresge Stamford S. S. Kresge New London

Kinus Radio Company. S. S. Kresge S. S. Kresge Champaign S. S. Kresge Springfield S. S. Kresge Peoria S. S. Kresge Freeport S. S. Kresge Belleville S. S. Kresge Danville S. S. Kresge Decatur Mid -West Radio Mart Chicago Newark Elect. Co Chicago

Chicago The Swords Company Rockford

Illinois Electric & Radio Supply Co -Chicago Grant Radio Co Chicago

Peoria Chicago

Pioneer Auto Supply Co

Indiana S. S. Kresge Evansville S. S. Kresge Fort Wayne S. S. Kresge Gary S. S. Kresge Lafayette S. S. Kresge South Bend S. S. Kresge Terre Haute S. S. Kresge Vincennes Kruse Radio Co Indianapolis

Iowa S. S. Kresge Davenport

1440 Broadway

Kentucky P. O. Burkes & Co Louisville S. S. Kresge

- Lexington

Louisiana Schuler Radio Svc New Orleans

Maine S. S. Kresge Lewiston S. S. Kresge Portland

Maryland A. R. Spartana Baltimore Mattson Radio Baltimore

Massachusetts T. F. Cushing Springfield H. Jappe Co Boston S. S. Kresge Boston S. S. Kresge Malden S. S. Kresge Quincy S. S. Kresge Springfield Mutty's Radio Labs Boston R. C. A. Institutes- Boston Trade Contact Corp Boston

Michigan S. S. Kresge Grand Rapids S. S. Kresge Highland Park S. S. Kresge Jackson S. S. Kresge Muskegon S. S. Kresge Saginaw R. & M. Radio Co Detroit Radio Distributing Co Detroit Radio Specialties Detroit Reno Radio Stores Detroit Wedemeyer Radio Co Ann Arbor

Minnesota Lew -Bonn Company St. l'auI Radio Maintenance Co....Minneapolis Southern Minn. Supply Co Mankato

Missouri Walter Ashe Radio Co St. Louis Burstein-Applebee Co Kansas City S. S. Kresge Hannibal S. S. Kresge Joplin S. S. Kresge St. Louis S. S. Kresge University City J. K. Gill Co Portland Van Ashe Radio Co St. Louis Johnson -Weller Co.. Inc Portianu

Nebraska S. S. Kresge Omaha

New Jersey Bennetts Radin Supply...Perth Amboy Jacksonfield Radio. -Camden, N. J. S. S. Kresge Morristown

New York American Sales Co New York City Baltimore Radio Co....New York City Bien, the Radio Man New York City Coast to Coast New York City H. L. Delis Co New York City Federated Purchaser, Inc.,

New York City Ft. Orange Radio Dist Corp...A.bany S. S. Kresge Dunkirk S. S. Kresge Buffalo S. S. Kresge Olean S. S. Kresgel Schenectady Kronson Bufrs,a Maurice Schwartz & Son.»Schenectady Radio Circular New York City R. C. A. Institutes New York City Roy C. Stage Syracuse Sun Radio Co New York Cita Wholesale Radio Service, Now York City

New Zealand Te Aro Book Depot Wellington

Ohio Aitken Radio Corp Toledo Burns Radio Co Dayton Goldhamer, Inc. Cleveland Hughes -Peters Elec. Corp Columbus Klarlae Radio Labs Kent S. S. Kresge Akron S. S. Kresge- Cincinnati S. S. Kresge Cleveland S. S. Kresge Columbus S. S. Kresge Marion S. S. Kresge Newark S. S. Kresge Toledo S. S. Kresge Sandusky S. S. Kresge Zanesville Lew Stores Toledo Progress Elec. Co Cleveland ltoss Radio Co Youngstown 'United Radio, Inc Cincinnati Uncle Sam Stores Akron

Oregon

Guarantee Pennsylvania

Cameradio Pittsburgh Hall's Harrisburg S. S. Kresge Butler S. S. Kresge 011 City S. S. Kresge Philadelphia S. S. Kresge Pottsville S. S. Kresge Reading S. S. Kresge Scranton S. S. Kresge Warren Keystone Radio Co Philadelphia Radio Elec. Service Ca Philadelphia M. & H. Sporting Goods, Philadelphia

Note :-A11 S. S. I{resge Stores are Green Front

If there is no dealer near you, order direct from us

Radio Treatise Co., Inc.

Rhode Island W. H. Edwards Radio Svc., Providence S. S. Kresge Pawtucket

South Dakota S. S. Kresge Aberdeen

Tennessee J. L. Perry Nashville

Texas Service Parts Co., Inc. Abilene Southwest Radio Svc Dallas Straus -Frank Co Houston Straus -Frank Co San Antonio Walter Tips Cu Austin

Virginia Johnston -Gasser Co Richmond S. S. Kresge Norfolk S. S. Kresge Richmond

West Virginia S. S. Kresge Charleston

Washington General Radio. Inc Seattle

Spokane Radio Co Spokane Wedel Co Seattle

Wisconsin Harriman Radio Sec Appleton S. S. Kresge ilwaukee Radio Parts Co Milwaukee

New York City

3 3

MMMMMMMMMMMMMMMMMMMMMMMMM MAR RAM M MMMMMMMMMNIMMIUMMMMMMMMMM MMMMMMMMMMMMMMMMMMMMMINMMMMMMe

SAY You SAW IT IN SERVICE

Ae O N LYzeetz. poLIJeAj GUARANTEED to q:r ACTUAL mom-wirz ¢ecep#ima. M1e

Features of the Scott Allwave Deluxe

15-550 Meters Includes major European, Asiatic, Aus- tralian, African, South American and Domestic voice stations.

Single Dial Tunes both R. F. and Oscillator circuits in perfect alignment automatic- ally from 15 to 550 meters-without trimmers.

No Plug In Coils Coils are not tapped. Entirely new system-actually MORE efficient than plug in coils.

New Class A Linear Amplifier

Gives perfectly uniform response to all frequencies from 30 to 8000 cycles at low as well as at high volume.

Twin Speakers Give actual reproduction to the perfect, linear output of the amplifier.

Non Oscillating 100 per cent shielding enables use of maximum sensitivity without annoy- ance of oscillation.

(-7L SCOTT ALLWAVE

DE LUXE

There is no question-no doubt-no gamble in the purchase of a Scott Allwave Deluxe. No mere hope, to be followed by bitter disappoint- ment. You KNOW-before you spend your money for a Scott Allwave Deluxe-exactly what you are going to get in performance. You KNOW you will hear England, France, Germany, Spain, Australia, South America and many more of the 300 intensely interesting foreign stations regularly received by owners of Scott Allwave Deluxe receivers. You know these things, before you buy because this receiver is positively guaranteed to give you actual world- wide reception ... every day ... regardless of which state you live in!

Why This Amazing Guarantee Is Possible

It might seem strange that no one else can offer the purchaser such absolute certainty of satisfaction on the subject of foreign reception. Yet it is not strange when all the facts are understood, because... only the Scott Allwave Deluxe has the electrical characteristics that make

possible an absolute guarantee of actual world wide reception. Only the Scott Allwave Deluxe has a sensitivity of 4-1000ths microvolt per meter at 1400 K. C.! That's one reason. The second is that the Scott Allwave Deluxe is the ONLY receiver having such a low natural noise level that the 4-1000ths microvolt per meter sensitivity can be used to yield loud, clear reception over distances up to 10,000 miles!

Send for PROOF! A great independent laboratory has charted the sensitivity, selectivity and tone of the Scott Allwave Deluxe. These charts PROVE, beyond any question of doubt that the Scott Allwave Deluxe will POSITIVELY give you the foreign reception you want ... the 90 channel broadcast selectivity you want, and the tone you want. Send today for this convincing PROOF ... then, you will understand fully why the Scott Allwave Deluxe is the only receiver that CAN be sold with a definite, unconditional guarantee of actual, world wide reception. Clip the coupon. Mail it at once.

THE E. H. SCOTT RADIO LABORATORIES, INC. 4450 Ravenswood Avenue Dept. S-82 ' Chicago, Illinois

E. H. SCOTT RADIO LABORATORIES, INC. 4450 Ravenswood Ave., Dept. S-82 Chicago, Ill.

Send me fully detailed technical description of the new Scott Allwave Deluxe.

NAME

/5-550 fritztezt, STREET

TOWN STATE

AUGUST, 1932 SAY You SAW IT IN SERVICE 187

AUGUST, 1932 Vol. 1, No. 7

SERVICE A Monthly Digest of Radio and Allied Maintenance

EDITOR John F. Rider

MANAGING EDITOR M. L. Muhleman

Editorial Contents FEATURES INDEX OF MONTHLY LITERATURE' 218

Kill That Noise 193

Biography: Rockwell M. Gray Resistance Measurement Method of Service

195 MANUFACTURERS

Analysis-Part III, By John F. Rider 196 American Photoelectric Equipment 216 Bradleyometer, Tapped 214 Continental Resistor Replacement Kit 216

ANTENNA (Editorial) 190 Eveready Raytheon ER -52 Tube 216 I.R.C. Power Wire Wound Resistors 214

AUTO -RADIO Oak All -Wave Switch Operadio Power Amplifier

214 214

Carter Genemotor Data 208

Interference Helps 208

Janette Auto "B" Diagrams 208 ON' THE JOB Reducing "C" Battery Voltages 208

Cognovit Notes (Announcement) 210 Form a Club. By W. O. Barnet 210

FORUM (The Reader's Page) 212 Profits in New Audio Channels. By C. L. Fairchild 210 Tone Quality-Satisfied Customers

By A. M. Hayes 210 GENERAL DATA

Atwater -Kent Chassis Specifications Atwater -Kent Resistance Values

202

202 PUBLIC ADDRESS Atwater -Kent Volume Controls 200 Class B Public -Address Amplifiers, Part II 204 Clarion AC -280 and 25-280 201 Measuring Pentodes with G.R. Mutual Conduct- Crosley Musicones, Adjustment 201 ance Meter 205 Crosley Receivers 200

Fada Models, New 202

Fada Notes Fada Speaker Fields. By L. J. Bell

200

200 SHORT WAVES

Hidden Condenser Short. By W. J. Gilliland 200 I -F. Interference 207 Kolster Rejectostatic K-140, K-142 198 Noise -Reducing Aerials.* By A. H. Lynch 207 Lock -In Systems* 201 Philco Models 4 and 4C Converters 206 Radiola 66 Resistance Data 200 Zenith Peak Frequencies 207

Advertising Director

ROBERT N. MANN 1440 Broadway, N. Y. City

Telephone: CHickering 4-4542

Published monthly by

John F. Rider Publications, Inc.

1440 BROADWAY NEW YORK, N. Y.

Officers JOHN F. RIDER,

President and Treasurer

M. L. MUHLEMAN, Vice -President

J. SCHNEIDER, Secretary

SERVICE, August, 1932. Volume 1, No. 7. Published monthly at New York, N. Y. Copyright, 1932 by John F. Rider Publications, Inc. Contents must not be reproduced without permission. Subscrip- tion price $1.00 per year in the United States of America; 15 cents per copy. $2.00 per year in Can- ada and foreign countries; 25 cents per copy. Application for entry as second-class matter is pending

188 SERVICE FOR

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The First ALL NEW

Set Tester Development

IN YEARS

THE ONLY SERVICE DEVICE MEASURING EVERY UNIT IN A

RADIO RECEIVER.

THE ONLY TESTER WHICH LOCATES EVERY DEFECTIVE RECEIVER UNIT when-

a THE RECEIVER IS

ENTIRELY INOPERATIVE.

D

A NEW METHOD

Rapid- Accurate-

Modern

WHAT IT MEASURES D

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Laboratory Accuracy

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Size: 12 1/16 x 13% x 3 inches

All Values of D. C. Volts on Quadruple Range Voltmeter from 0 to 1000 Volts-High Sensitivity Voltmeter, 1666 Ohms per Volt. Ranges 0 to 20, 0 to 200, 0 to 500, 0 to 1000 Volts.

All Values of A. C. Volts on Quadruple Range A. C. Voltmeter 0 to 800 Volts. Ranges 0 to 8, 0 to 40, 0 to 160, 0 to 800 Volts.

All Values of D. C. Milliamperes on Double Range Milliammeter from 0 to 200 Milliamperes. Ranges 0 to 40, 0 to 200 Milliamperes.

All Values of A. C. Milliamperes on Double Range Milliammeter from 0 to 200 Milliamperes. Ranges 0 to 40, 0 to 200 Milliamperes.

All Values of Resistance on Triple Range Ohmmeter from 1/ Ohm to 20 Megohms. Ranges 4 to 1000, 200 to 200,000 Ohms, and 2000 Ohms to 20 Megohms.

All Values of Capacity on Double Range Capacity Meter from .05 to 15 Micro Farads. Ranges .05 to 1 M.F., 1/4

to 15 M.F. Capacities from .0005 to .05 measured on Megohmeter. Tests. ELECTROLYTIC CONDENSER LEAKAGE AND CAPACITY UNDER OPERATIVE CONDITIONS. OUTPUT OF RECEIVERS MEASURED ON MILLIAMMETER.

All Values of Inductance on Double Range Inductance Meter from 1/2 to 50 Henries. TESTS RADIO TUBES BY THE MOST ACCURATELY KNOWN METHOD BY APPLYING STANDARD

VALUES OF D. C. VOLTAGE TO PLATE AND GRID, READING STANDARD VALUES OF PLATE CURRENT, MUTUAL CONDUCTANCE AND GAS CONTENT.

All measurements without use of Auxiliary Apparatus. Instructions include Loose Leaf Book in Leatherette Binder covering. Point -to -Point Resistance Measurements on Receivers.

List Price - - - - $250.00 Carrying Case - - - - $15.00 Subject to Regular Discounts SERVICE MEN-WRITE NOW TO

THE HICKOK ELECTRICAL INSTRUMENT CO. 10516 DUPONT AVENUE CLEVELAND, OHIO

AUGUST, 1932 SAY You SAW IT IN SERVICE 1 8 9

THE ANTENNA ... HOW about carbon resistors? The service industry as a

whole is interested in learning more about the testing of these units. At the present time we know that wire - wound and metallized resistors may be checked at any value of voltage within the wattage rating of the unit without fear of unjust condemnation of the unit on the grounds that the measured value shows some deviation from the rated resistance, due more to the testing circuit rather than the resistor itself.

At the present time there is no doubt about the fact that the voltage co -efficient of carbon resistors results in variations occasioned by the testing voltages, and that carbon resistors are unjustly condemned. What are the correct voltages which should be applied to carbon or composition resistors during the process of testing in order to ascertain the accepted value of resistance for that resistor? In contrast to other types of resistors, the wattage rating is not the de- termining influence, that is, as far as testing in the field is concerned. The variable current flow which may occur when various testing voltages are applied, all within the wattage rating, will result in various values of resistance.

In due justice to the instrument manufacturer, the Service Man, the receiver manufacturer, the customer and the carbon resistor manufacturer-all of whom are vitally concerned when a carbon resistor employed in a receiver is being tested for its ohmic value-the service industry would like to know what value of test voltage to apply to carbon resistors of various ohmic values and various wattage ratings. This information is of paramount importance when an ohmmeter is being applied to a receiver. Particularly so when ohmmeters are being made with increased resistance scales, which require higher, than customary voltages to extend the range into megohms.

The RMA Engineering test standards as applied to composition resistors cover the subject in an elaborate and comprehensive fashion as far as engineering is concerned, but as

can be expected, in view of the fact that it is out of their sphere of operation, they do not cover the subject from the angle of resistance measurement in the field by the Service Man.

The service industry at large admits the need for counsel in this direction and no one is better fitted to furnish this advice than the people who produce the products.

MORE and more we note the trend towards resistance measurement methods of service analysis. Ever since

the exploitation of this idea in the editorial and text pages of SERVICE, we have been receiving letters to the effect that more and more men are using the system and that a

large number have been using the system in the past. The old timers welcome the "push" behind the system as vindi- cation of their ideas.

In the meantime, the subject is receiving attention from the receiver manufacturers and an increasing number of the present crop of service manuals are devoting space to resistance measurement data.

A critical examination of the present (1933) output of radio receivers, low as well as high priced, shows the definite

need for resistance measurement methods of service work. The increased complexity of receiver design with increased sensitivity, automatic volume control, etc., requires more extensive isolation of the respective circuits. This isolation is secured by means of grid and plate filter resistors. The presence of these high -resistance units definitely interferes with the exact determination of the effective voltages applied to the respective tube elements. This fact has been long established, but it is of greater interest today because every major receiver manufacturer employs grid filter and plate filter resistors, and if indications are a barometer, then more resistors will be found in future receivers.

There is no doubt about the fact that future receivers will be more expensive than present-day receivers. Higher sales prices are required for the survival of the industry. Higher sales prices are invariably accompanied by a greater number of tubes. The 10, 12, 14 and 16 tube receivers displayed at the show are forerunners in this field. Any receiver with this number of tubes must be well designed to remain stable in operation. Stability requires isolation of circuits. Isola- tion means the use of resistors. The greater the number of high -resistance units in circuits which involve voltage measurement, the more logical is the need for resistance measurement as the conclusive test.

AERIALS are being neglected. Perhaps this may sound old-fashioned in this day of highly sensitive receivers,

as well as the comment by the dealers' salesmen that, "this receiver will operate without an aerial." But the fact remains that the aerial is still a necessity for consistent and satisfactory reception. It is much better to operate a receiver at a low volume level with an aerial and to have noiseless higher volume available when desired, than to operate a receiver almost wide open without an aerial and have a noisy system when "full on" for some special occasion.

Because of high receiver sensitivity, any type of aerial is considered as being satisfactory. That is incorrect. A poor aerial is worse than none because it may lead to undesired consequences. One of these is noise. The other is poor sensitivity. There still are many locations where nothing but a good aerial will produce good results. Good aerials mean just that. Slipshod erection, insulation and grounding may be inexpensive at the outset, but expensive later. The newer type of noise -reducing aerials must be of good construction to be effective. Give the receiver manufacturer and the customer a break. Give them what they are entitled to receive -a good installation.

WE are pleased to see that the advertising in this issue is of special nature. Examine it ... you will see that

100% of the copy is written for the Service Man. All of the products and literature offered are prepared exclusively for you.

John F. Rider.

190 SERVICE FOR

SERVICE Equip You SERVICE

SHOP!

Oscillator and Output Meter Service men! You can't service super hets properly without this meter! Absolute necessity for up-to-date servicing. Free with small purchase of National Union Tubes.

Two Service Manuals Volume 1 and Volume 2 above are written by J. F. Rider, radio scientist and lecturer. Vol. 1 contains over 2,000 diagrams on voltage, electrical values, color coding, peculiarities of receivers, amplifiers, and eliminators. Vol. 2 has more than 700 pages of valuable information. For the first time receivers are broken down and point-to-point resistance data is furnished, which makes possible the operation of the continuity, capacity, and resistance tester at the right. Free with small purchase of Tubes.

FREE ! Tube Base Layout Chart compiled by John F. Rider-absolutely no obligation-write for one!

National Union, maker of the famous National Union Radio Tubes, is continuing this amazing free offer a few weeks longer. Radio men! Here's equipment every live - wire, up-to-date service man must have! You can have absolutely free any one or all of the equipment featured in this ad- vertisement ... with a small purchase of National Union Radio Tubes. Think of it! 5 pieces of valuable equipment that are indispensable to any service man. Equipment that will save hours of time ... and make more profits! So take advantage of this opportunity at once! Read the details about this equipment, then mail the coupon below at once !

NEW ! LATEST

METHOD OF SERVICING!

New Readrite Continuity, Capacity and Re- sistance Tester! No more chassis pulling! With the new Readrite Resistance Tester you can make every test, continuity, capacity, and resistance . . . without taking the set apart! Operates easily, quickly, efficiently. And that means more profits to you! Yours free with purchase of moderate amount of National Union Tubes, and small deposit.

The Readrite Tube Tester Compact, easily carried. No more squint- ing in dark corners! This tester has an illuminated dial which shows reading in even darkest corners! Hundreds of service men have already learned what this tester has meant to them in more profits! Yours free with purchase of small quantity of National Union Tubes.

NATIONAL UNION RADIO CORPORATION 400 MADISON AVENUE NEW YORK CITY Dear Sirs: Please tell me how I can have above equipment free. I am checking those in

which I am interested: READRITE TUBE TESTER OSCILLATOR AND OUTPUT METER VOL. 1 VOL. II

READRITE RESISTANCE TESTER

NAME

ADDRESS CITY STATE


REPLACEMENT PARTS HEADQUARTERS

Your customers depend upon you for good service. Your success depends upon your own efforts and the suitability of the replacement parts you use. When you come to replacement parts headquarters you can depend upon efficiency, long life and complete satisfaction of any parts you specify. Your customers can depend upon you for all 'round satisfaction. And you can depend upon their continued custom and good -will.

With the development of Mallory-Elkon condensers the user is now assured of characteristics and performance never before obtainable. The efficiency of Mallory-Elkon condensers from the standpoints of power factor, leakage, permissible overload voltages and life has been definitely and widely established. Mallory- Elkon Condensers in metal cans are available in either the upright or the inverted type. Mallory-Elkon By -Pass Condensers are becoming increasingly popular. Write for our latest bulletin showing the' right condenser to replace in each set.

Showing the dependable built-in switch and resistance securely housed in the Bakelite base, safe from accidental damage.

The combined knowledge, experience and resource- fulness of two distinguished radio engineering groups are responsible for this most valuable contribution to the science of volume control. Yaxley engineers developed the principle, Yaxley engineers and Mallory engineers carried it to a point of practicability that brings to the industry a degree of volume control performance now attract- ing nation-wide attention. You will be quick to appreciate the advantages of

The contact arm is of new andimprovedconstruction. The pressure is always uniform-the action smooth

and silent.

this extremely flexible wire wound volume control with inclosed switch (listed as standard by Under- writers' Laboratories) and contact arm, insulated or grounded style optional. This control is of unusual compactness and has a minimum number of parts. The simple, efficient switch, of the rotary "click -on" type is especially desirable ... and the new resistance coil assures smooth operation. Write for Bulletin which shows the right Yaxley replacement control for each set on the market.

And don't forget to write, for full details covering the Mallory- Elkon "B" Eliminator that has made auto radio all electric.

Service Men The Country Over Use These Yaxley Replacement Parts

Volume Controls, Rheostats, Potentiometers, Short and Long Wave Switches, Radio Con- venience Outlets, Resistances, Jack Switches, Push Button Switches, Tip Jacks, Phone Plugs.

P. R. MALLORY & CO., Incorporated, INDIANAPOLIS, INDIANA 192 SAY YOU SAW IT IN SERVICE SERVICE FOR

Kill That Noise . . AGREAT amount of effort is being made to either

reduce or eliminate both natural and man-made electrical interference from the provinces of radio

waves. This effort to clear the "air" of extraneous noises on the one hand and to incorporate noise -reducing systems in antenna circuits and radio receivers on the other hand is worthy as a beneficent cause in the name of better radio. Possibly this noise -reducing movement was first prompted by a growing impatience on the part of the listening public (for the impatient public is always with us, as are the rich) .

Be that as it may, the success of the whole movement is de- pendent almost entirely on the Service Technician, who is the only one in a position to take care of individual cases.

This article is our slight contribution to the cause. Much of the material has been written (and re -written) before and therefore may be old news to you. Some of the material is rather new, while other bits are of little value except where the set owner is sufficiently solvent to stand the expense of an elaborate "noise catcher."

WHY NOISE ANYHOW?

Electrical interference is generally due to small arcs or sparks, or to devices such as switches and certain types of rectifiers which suddenly make or break a current -carrying

ANTENNA

200 MMFD 1000., AT LEAD 0? COPPER SHEATH 300 METERS C.

N/GH

RECEIVER POSTS .

H/GH v

1000.,

Here are the details of a typical noise -reducing transmission line, using shielded lead-in wire in connection with two impedance -matching transformers. The 1000 -ohm termination resistance across the aerial and ground posts of the

receiver is used only with low -impedance inputs

circuit. A great deal of such man-made interference is radi- ated into the ether directly by the apparatus causing it, and by the associated wiring. Since the high -frequency components of such interference represent a small amount of power, and since the effective height of the radating mem- bers (apparatus frames and wiring) is usually small, the effective range of man-made interference is limited to a rela- tively small area in the vicinity of the offending equipment. This is rather sporting of the equipment, but the equipment, like anxious candidates, has a way of gathering closely around the radio sets. It must be a part of the scheme of life to have all noise -making devices as near the radio as possible.

It is a fact that certain types of interference are transmitted along the power lines and as a result such lines may radiate interference or conduct it directly to the radio receiver. But this usually accounts for a very small amount of the pickup and in most cases may be discarded with a snap of the fingers because most modern sets employ static shields between the primary and secondary windings of the power transformer. These shields effectively reduce the amount of such interference that enters the receiver through

POWER L/NE

--10FT CL/RTA/N--

15FT

1J4ll_i_ ANTENNA

- oTitt

F/G. 2A.

An antenna can be shielded from power -line interference by the use of an "electric curtain." Details of such curtains

are given in Figs. 2E and 2D

the power supply. In other receivers a small buffer condenser is frequently employed to short-circuit such intereference back to the ground side of the power line from whence nothing returns.

Here is another point to consider in connection with the same sort of racket: The power transformers in most receivers have the primary winding near the core and the outer layers (the layers of the primary nearest the secondary) are tapped for various power line voltages. When this is the case and the full winding (highest line voltage tap) is not used, the outer layers of the primary will act as a static shield if this side of the primary is connected to the ground side of the power line. Reversing the power plug to reduce interference is now such common practice that this connection quite generally obtains. There is, therefore, little chance for interference to slink its way into the radio receiver via the power supply.

Of course, similar interference may be picked up by exposed circuit elements in the radio receiver, but this is cer tainly not apt to happen in modern receivers for, unlike modern bathers, nothing worth looking at is left exposed. In some of the less modern exposed receivers it may be desirable to shield some of the circuit elements to prevent this condition. However, it is seldom that such precautions are necessary.

LO-THE ANTENNA!

Undoubtedly the most effective method of minimizing interference lies in providing a stronger, interference -free signal. This requires first a high antenna located in a posi -

Electric curtains should be higher than both the aerial and power wires, and should always have a length exceeding the effective component of the aerial parallel to the power line

POWER L/NE

CL/RTA/N ..., f+-- 507T.

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ANTENNA

CURIA/N'`

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ANTENNA

F/G. 2C.

AUGUST, 1932 193

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This sketch, and that of Fig. 2D below, give the details of effective "electric curtains." It is seen that they are made up in the form of a wire grid. In both cases the wires represent

a single conductor

tion free from interference, and a shielded lead-in to conduct the signal to the receiver through the interference -in- fested areas.

There is a great deal of misinformation on antenna construction. For broadcast reception a single horizontal wire about 100 feet in length is probably the best answer among known antennas. Either an L or T type is satisfactory, that is, either an aerial with the lead-in from the center, or an aerial with the lead-in from one or the other end. It is a common error to assume that antenna performance depends upon the number of feet of wire employed in its construction, regardless of how the antenna wire is run. A zig- zagging or curved antenna should always be avoided since in most cases it will reduce rather than increase the signal. Thus, the voltage induced in the two legs of a V-shaped antenna with lead-in at one end will subtract and the re- sultant voltage is often considerably less than that from but one leg of the V alone.

The antenna should always be as high as possible and should be run at right angles to power or telephone lines. It should not cross above or below such lines. If erected in the back yard it should be several feet above the tops of neighboring trees. If on the roof, it should be kept as far as possible from all metal parts of the building, as such parts are capable of re -radiating interference. Metal roofs should always be grounded. Really good insulators should be used at each end of the antenna and should be placed 5

or 6 feet from their supports. And, of course, all joints should be carefully soldered.

SHIELDED LEAD-INS

The shielded lead-in may consist of an insulated copper wire shielded with copper braid or a lead sheath. ("Wire -

COPPER kV/RES..... ir v

r .um.

>

.

/zeo/ 0 , 5 A / ' /sh "I_( Av " .

METAL PIPES DRIVEN SEVERAL FEET INTO SOIL

. .. FIG 20.

mould" lead sheathed wire may be used satisfactorily.) The lead sheath is preferable since it is a more effective static shield and will, therefore, be more effective in eliminating interference than with the copper braid. The shield should be grounded at a number of points along its length if possible. (See Fig. 1) . Otherwise it should be grounded at the receiver end only. The sheath should start as close to the antenna as possible and should be continued to the ground binding post of the receiver.

SIGNAL LOSS

Of course, there is a sizable loss of signal in a shielded lead-in. In the usual shielded lead-in this may amount to 90 per cent or more of the signal picked up by the antenna for stretches of 100 feet. This loss is seldom serious, since it is usually more than offset by the additional signal picked up by a good antenna. However, if the shielded lead-in is con- verted into a transmission line (a la Bell Tel.) by the simple procedure of providing impedance -matching transformers at the antenna and receiver ends, the signal loss in the lead- in may be reduced to say 5 per cent of the signal in a 100 -foot length. (Impedance -matching transformers are very

SPAR/f KILLER F/G. 3.

( " "0 1MF T 100 M/CROHENRYS

70 1 M/[[/HENRY RF CHOKES

1MFT oóooJ

POWER Li/YE FILTER

The arrangement shown in Fig. 3 is effective for most any type of make -and -break circuit. The circuit of Fig. 4 will

quell line surges

successful if correctly designed.) As an example, an aver- age antenna 20 feet in height and 100 feet in length has a capacity of about 200 micro-microfarads, an inductance of 20 to 40 microhenrys and a resistance of probably 50 ohms. At 1000 kc. (300 meters) this antenna impedance is therefore about 1000 ohms. A long transmission line, or a short one properly terminated in a resistance, has an impedance of about 50 ohms. There are several transformers on the market, any one of which will step-up the transmission line impedance to about 1000 ohms. The induced antenna voltage will then be divided between the 1000 ohms capacity reactance of the antenna and the 1000 ohms resistance pre- sented by the antenna transformer. That is, about 70 per cent of the induced voltage will be developed across the transformer primary.

If a similar transformer is connected between the transmission line and radio receiver and a non -inductive resistance of 1000 ohms connected across the radio receiver terminals, 70 per cent of the antenna voltage will again appear across the receiver terminals, neglecting line losses, which are of the order of 4 or 5 per cent for a 100 -foot length of line. The complete arrangement is shown in Fig. 1

It is a fact that most modern receivers have a high -impedance input, usually 1000 ohms or more, and while this impedance is not entirely resistive, it is frequently a satisfactory termination for the transformer, so that the 1000 - ohm resistor may be omitted. For short lines of 150 feet or

194 SERVICE FOR

less, it is' usually advantageous to omit the termination resistance. If a lead sheath cable is used it is always advantageous to bury it, and thus in addition to insuring a good ground reduce the interference pickup considerably by the additional shielding of the ,surrounding earth. In some instances it may be deemed satisfactory to omit the transformer at the receiver end of the line. This will usually reduce the received signal from 70 per cent of the antenna voltage to about 25 per cent. If the antenna is located in a space rela- tively remote from interference, such a setup is entirely satisfactory.

SOURCE CURES

A last resort in dealing with interference lies in effectively suppressing it at its source. Since there are usually so many interfering devices in any one locality, this is frequently both difficult and expensive. A certain amount of this sort of thing cannot be avoided, however, since in some cases it is impossible to select an antenna location sufficiently remote from all interference -generating devices. Shielding of the noise -making elements is probably the most effective pre -

A very effective arrangement for use with motor -generators and converters. Note that the frame of the machine is

grounded

ventive measure that can be applied. Of course all metal frames and casings should be carefully grounded.

Interference from overhead trolley and power lines can often be reduced by suspending a number of grounded ver- tical copper wires between the power line and the antenna. (See Figs. 2-A, B, C, D, and E.) The spacing of these ver- tical wires depends on the intensity of the interference, a horizontal separation of one or two feet being quite a common procedure. This so-called curtain should be somewhat longer than that component of the antenna parallel to the power line (see Fig. 2-B) and should be higher by a few feet than either the power line or antenna, if possible.

In Figs. 3 to 7 are shown some common types of interference -suppression devices, most of which are self-explana- tory. Radiation from the spark plugs of an internal corn -

R -F. chokes should be used in the anode leads of mercury- vapor rectifiers to eliminate possible interference from r -f.

surges produced at critical voltage points

!'ROUNDED SHIELD

F/6 E TUNGAR OR MERCURY VAPOR RECTIFIER FILTER

1 NOTE. - CONDENSER

. LEADS M(I57 BE SHORT AND DIRECT

TONGAR OR MERCURY VAPOR RECTIFIER FILTER.

The effectiveness may be increased by the addition of condensers. The r -f. chokes and rectifier tube should be

enclosed in a grounded shield, as in Fig. 6

bustion engine may be naturally reduced by insertion of a series resistance of sufficient value (usually 20,000 to 50,000 ohms) to damp out oscillation after the initial spark has ceased. A similar result may be accomplished by inserting a shielded r -f. choke in series with each spark plug.

Brushes and brush holders of motors should be thorough- ly inspected at regular intervals to prevent dirty contacts or chattering brushes. Belting used with insulated pulleys and shafting will frequently collect a static charge which may periodically discharge to nearby conductors. This may be eliminated by collecting the belt charge by means of a grounded metal brush contacting the belt. Metal shafting should also be carefully grounded by means of a wiping contact. In a similar manner the shaft of a motor or generator may become insulated from the bearing by a film of oil or grease and thus cause interference due to the collection and discharge of a static charge. In such cases the most effective remedy lies in the use of a grounded wiping contact on the shaft.

In general it is always good practice to ground any metal frames, cores, etc., carefully and to shield leads to and from devices causing interference, even though other suppression measures have already been employed.

Accidental or intermittent grounds due to various factors are one of the most frequent causes of trouble and are eliminated either by grounding the floating element or prevent- ing the intermittent ground. Obviously, the latter may be difficult to locate.

OdQeOn

The Man on the Cover Rockwell M. Gray

Assistant Manager, Silver -Marshall

ROCKWELL M. (ROCKY) GRAY is one of the most colorful figures in the radio industry. He is a down -

easterner who still says "idear." A graduate of the Boston University. Ex -radio dealer and star jobber salesman-all before he became one of Silver -Marshall's first employees. He held the position of New England District Manager from 1926 to 1930, when he was called into the factory as Assistant Manager of the Parts Division. For the past year he has had complete charge of parts, kits, the chassis and sound equipment divisions.

He is an engineer, a crack salesman, a good manager and not nearly as hard-boiled as he looks.

AUGUST, 1932 195

Resistance Measurement Method of Service Analysis

By JOHN F. RIDER

PART I I I

THE application of point-to-point resistance measurement to d -c. operated receivers differs very little from the process of analyzing an a -c. receiver. There are

some few minor variations, but on the whole, the test is the same. It is this feature of versatility which makes the re-

sistance measurement method of service analysis so valuable. As to reference points, the chassis is still the major one.

Supplementary to the chassis, we have the negative and the positive power plug lugs. Of these two, the negative lug is invariably common to the chassis, so that the reference points are not more than two in number. In this manner the rectifier filament in a -c. circuits is replaced by the positive lug of the power cable plug in d -c. circuits.

The removal of the speaker or speaker field is the same in all types of circuits. It is possible that the opening of these circuits may interfere with the continuity of some other circuits in the receiver, but the exact condition is a variable, depending upon the design.

At first glance the resistance network in the diagram shown in Fig. 1 is quite confusing. A simplified version of the various resistors and chokes, with the exception of the heaters, is shown in Fig. 2. All of these units bear the same relation to each other as indicated in the schematic diagram of Fig. 1. As is evident, any of the tube elements can be utilized as the secondary reference point with re-

spect td the plus or minus lug upon the power plug, or the chassis, which is also joined to the negative power lead through the 1 -ohm choke.

Once the test points have been established, the testing of the circuits remains identical to any a -c. circuit. It is necessary to mention that there exists the possibility of a

more complex circuit in a d -c. receiver than in an a -c.

receiver. This for the reason that some of the filaments or heaters have shunt resistors. Also because of the division of the power -line voltage between filaments or heaters, the plates and the speaker field. In a -c. circuits, the heater- and plate -voltage are secured from separate sources. In d -c. circuits they are secured from a common source. But with the tubes removed in d -c. systems, the entire heater circuit is eliminated and testing of the plate and grid circuits can progress without further trouble or worry about the heater systems.

If you will examine Fig. 2, you will note that the dis- tribution of the plate voltages takes place by means of a voltage divider, connected across the power -supply line, just as if that system were the power pack filter output in an a -c. receiver. Generally speaking, this method of dis- tribution is employed in the majority of modern d -c. receivers, but is not necessarily true in some of the older receivers. Even when not used, analysis is no more diffi-

Fig. 1. Schematic diagram of Kolster D -C 83 and 93, discussed in the text

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196 SERVICE FOR

cult. Whether it is, or is not used, the sole difference lies in whether or not any one tube element is directly connected to the plus as well as the minus lugs upon the power cable.

In Fig. 1 we can check the resistance between the output tube plates and either the plus or minus lug upon the power plug. However, if a voltage divider were not used -that is, the connection to the negative power lead would be the midtap upon the output tube heater or filament and the plate voltage were secured directly from the plus power plug lug-there would be no direct connection between the plate terminal upon the output tube socket and the negative lug upon the power plug when the output tube was out of the socket, or inoperative. A circuit such as described is the duplicate of the early type a -c. systems wherein the various plate voltages were secured via individual resistors connected between the various tube plates and the "high" lead of the power pack filter.

CIRCUIT CHECK

Let us check some of the tube circuits shown in Fig. 1.

The initial requirements for a d -c. receiver to be checked by means of resistance measurement are as follows:

1. Test all tubes independently of the receiver. 2. Measure the line voltage. Disconnect all batteries. 3. Test aerial and ground system. 4. Check the output transformer and speaker voice coil

systems. 5. Remove all tubes from the receiver. Remove the

pilot light. Disconnect the speaker inclusive of the voice coil. If the output transformer is a part of the speaker and its plug is connected the plug, thus opening thé output tube plate circuits and also the field system. It is possible that a separate plug is

provided for the field coil. Assuming that the above has been completed and the

tests indicate that the fault is in the receiver proper, we would work along the following lines.

From chassis to: R -F. Control Grid-Slightly more than 1. megohm.* *The input circuit of the r -f. stage is so arranged that a direct

circuit through the two, r -f. coils is not possible when working between the control grid and the chassis. Only one coil, that nearest the control grid, can be checked through the 1. meg. resistor. Of course, one cannot expect to note a variation of 3.2 ohms in 1,000,- 000 ohms so that it would be necessary to separately test the two coils by checking between the control grid and the stator of the first tuning condenser TC -1.

R -F. Cathode (V.C. Max.) R -F. Cathode (V.C. Min.) R -F. Screen Grid (V.C. Max.) R -F. Plate

300 ohms 2,151 ohms

16,851 ohms 26,877 ohms*

*Since we are checking the continuity of the r -f. plate winding, a supplementary test is required to show the resistance of the r -f.

plate winding. Such a test would be from:- R-F. Plate to '47 Screen Grid 26 ohms

The last named test is preferred to a test between the r -f. plate and the plug lug upon the power plug cable, because the latter includes two additional units, namely the 1. -ohm r -f. choke in the plus power lead, and the 85 -ohm filter choke.

Proceeding to the next tube, the test between the tube elements and the chassis continues:

1st Detector Control Grid 26 ohms 1st Detector Cathode 10,000 ohms*

*This resistance should really be 10,003.9 ohms, since the coupling coil of 3.9 ohms is in series with the 10,000 ohm resistor.

However, we cannot hope to discern a discrepancy of 3.9 ohms in 10,000, hence it is necessary, in order to check the d -c. resistance of the coupling coil, to test across its terminals. Continuing:

1st Detector Screen Grid 16,651 ohms 1st Detector Plate 26,901 ohms*

*Once more it is quite difficult to detect any error in the d -c. resistance of the i -f. transformer primary located in the 1st detector plate circuit. Consequently, it is necessary to test this winding by working between the plate of the 1st detector tube and the output tube screen grid, thus:

1st Detector Plate to '47 Screen Grid -50 ohms* *Now, we find that the resistance between these two points is

substantially zero, although the rated value is 50 ohms. There is no doubt about the fact that the trouble is related to this winding. Maybe the shunt condenser is shorted or the wihding itself is shorted. Whichever it is, it is not the best practice to immediately desist making further tests. It might be best to complete a routine test of the remainder of the circuits. While it is true that troubles are, as a rule, singular in number, still one can never tell. As it happens, the nature of this fault is such as to be free of an influence upon the other circuits in the receiver, so that all further tests can be made without considering the probable effect of the short circuit.

The balance of the tests follow as outlined, so that there is no need for duplicate explanation, with the exception of the filament circuits. We note that with the tubes in their sockets, the various heaters and filaments are in series, but that the circuit is not closed unless the speaker plug is inserted into its socket. By checking the speaker field independently of the balance of the receiver and then testing between the negative power plug lug and the correct contact upon the speaker socket, we can check the resistance of one leg of the entire filament system. For that matter, it is possible to check the important control resistors in the filament circuit without ever inserting the tubes into their sockets. Thus the r -f. choke in the negative leg can be checked by operating between the negative lug upon the power plug and the chassis. The 30 -ohm resistor can be tested by checking across the pilot light terminals and the 60 -ohm control resistor can be

tested by working between the pilot light and the correct lug upon the speaker socket. Between one pilot light contact and the speaker socket, we include the pilot light resistor and the other control resistor and between the other pilot light contact and the speaker socket lug, we include only the 60 -ohm control resistor.

(This series is to be concluded next month with an article on electrolytic condensers present in resistance - measured circuits. The condenser tester mentioned in an earlier installment of this series will also appear in the September issue. Editor) .

Fig. 2. Equivalent network of the power -supply filter and voltage -dividing resistors of the circuit of Fig. 1

OUTPUT TUBE PLATE VOLTAGE

OTHER PLATES AND OUTPUT SPACE VOLTAGES.

DETECTOR PLATE

SCREEN VOLTAGES

DETECTOR CATHODE

AUGUST, 1932 197

General Data . .

Kolster Rejectostatic K-140, K-142 The Kolster K-140 is for operation on a

110 -volt, 60 -cycle line, while the K-142 is for operation on a 110 -volt, 25 -cycle line. The changes in the power -supply equipment for these two models are indicated on the accompanying schematic diagram. It should also be noted that the resistance values of all units, including transformers and coils, are given in the diagram, which permit the point-to-point resistance measurement method of servicing. The actual continuity test data is given in Table 1. As an added as- sistance in checking, the color coding for both condensers and resistors are included with the diagram.

THE CIRCUIT

The superheterodyne circuit is used, and employs type 58 tubes as first r -f., first detector, first i -f. and second i -f. A type 56 is used as second detector and automatic volume control, and a second type 56 employed as intermediate audio -frequency amplifier with manual volume control and "Radio" - "Phono." switching in the grid circuit. A third 56 tube is used for the oscillator and two 47 tubes are used in push-pull in the power stage which feeds twin speakers. Note

from the diagram that the smaller of the two dynamic speakers plugs into a receptacle located on the larger speaker, from whence there is a cable for simultaneously plugging both speakers into the outlet on the side of the chassis.

EXTERNAL CONNECTIONS

The radio -phonograph switching arrangement may appear a bit confusing. Referring to Fig. 1, the phonograph attachment plate is shown mounted on the rear wall of the chassis. The pickup leads should be connected to posts 1 and 3. When the jumper connects posts 1 and 2, the set is in readi- ness for phonograph reproduction. When the jumper connects posts 1 and 3 (as shown) the phonograph pickup is shorted out of the circuit.

In this same sketch the short-wave adapter socket is shown. This same socket is also shown in the schematic diagram, to the right of the pilot light.

TUBE SHIELDS

When taking out tubes in either of these models, remove the tube shields very carefully. Make sure that the grid leads are disconnected from the caps on top of the

ANTENNA

4F ANTENNA REJECTOSTAT Jee Fig 2

fB GROUND PLATE, Water Pipe, etc.

Transmission (ine Cable can be buried or run to house under eaves. etc.

ririf7.171 I W POWER LINESuii

keep antenna away from them.

TO RADIO RECEIVER --REJ ECTO STAT ----------

Fig. 2. A typical installation. The aerial should be free of power lines,

etc., and free of any obstructions

tubes which utilize them and are pushed through the openings in the sides of the tube shields through which the leads run. Do this before attempting to lift any of the "58" shields. These "58" tube shields have an internal partition shield. It is of equal importance that these particular shields are

Schematic diagram of Kolster Note the unusual plug connections. The filter choke in the power - supply circuit has a resistance of 85 ohms, with a tolerance of plus or minus ten percent

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N-140 SO.60N 0 A-56],01 ..7777 K-142 25600. A-600.010 RESISTOR COLOR CODE '

VALU ELODY- TIP DOT 500 GREEN BLACK BROWN 750 VIOLET GREEN BLACK 3.000 ORANGE BLACK RL0 _

5000 GREEN BLACK RED 10.000 BROWN BLACK ORANGE

10000-1W BROWN BLACK ORANGE

25000 REO GREEN ORANGE

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CAPACITY COLOR CODE CAPACITY COLOR

0000 0005 0001 riZteif 01 x:;---

198 SERVICE FOR

GENERAL DATA-continued

used over the "58" tubes, and not confused with the shields used over the "56" tubes.

The pilot light used in the K-140 and K-142 is a Mazda Type 41 with a 2.5 -volt filament.

THE REJECTOSTATIC SYSTEM

The Rejectostatic System is and is not a part of the receiver proper. It is in the sense that the entire chassis, including the tubes and all coils, are shielded against pickup beyond the usual measure. It will be noted from Fig. 1 that the antenna and ground leads from the antenna transformer are also shielded, and from the circuit diagram that the primary of the antenna transformer is ungrounded. This latter measure is taken so that there is no chance of any power line interference, etc., of being impressed on this input circuit and thereafter amplified by its passage through the other circuits. And incidentally, since this primary is ungrounded, a separate ground connection is necessarily added to the short- wave adapter socket to provide a return path for the "B" current.

Fig. 1. Chassis layout of the K-140. When using the Rejectostat, extra shields are placed over the usual '58 tube shields. The arrows indicate the location of the

four tubes so treated

The remainder of the Rejectostatic System is external to the set and does not necessarily have to be used. Nevertheless, it is very effective and if there is bothersome noise in the vicinity of the aerial, it is advantageous to use the system.

The Rejectostatic System is composed of the usual form of aerial 75 to 200 feet in length (not counting length of lead-in) which should be erected in a location as free from electrical disturbances as possible, and strung at right angles to any power lines. A typical residential installation is shown in Fig. 2.

TABLE i

Reference Points Value in Ohms Reference Points Value in Ohms Aerial to ground 31 2nd det. grid r -f. choke only 150

From Chassis to: * 2nd det. control grid to plate 0 R -F. control grid 1 meg. 2nd det. cathode 0 R -F. grid coil only 4.5 R -F. cathode 500 Osc. control grid 100,000 R -F. screen grid 25,000 Osc. cathode 0 R -F. plate 60,002.6 Osc. plate 75,001.9 R -F. plate to neon lamp 2.6 Osc. plate coil only 1.9

Osc. grid winding only 3.4 1st det. control grid 1 meg. 1st det. control grid to 2nd tuning 1st a -f. control grid

condenser stator 9.4 (V.C. max.) 500,000 1st det. cathode 3,002.6 1st a -f. cathode 5,000 1st det. screen grid 25,000 1st a -f. plate 76,650 1st det. plate** 60,054 1st a -f. plate to '47 screen 26,650 1st det. plate to r -f. plate 56.6

1st i -f. control grid 1,000,054 ist i -f. cathode 750 1st i -f. grid coil only (i -f.

trans. sec.) 54 1st i -f. screen grid 25,000 1st i -f. plate*** 60,054 1st i -f. plate to 1st det. plate 56.6

2nd i -f. control grid 1,000,054 2nd i -f. grid winding only 54 2nd i -f. cathode 750 2nd i -f. screen grid 25,000 2nd i -f. plate 60,054 2nd i -f. plate to r -f. plate 56.6

2nd clet. control grid 500,204 2nd det. grid winding only 54

*Measurements should be made with all tubes out of sockets and both speakers disconnected. Neon lamp removed from socket and short-wave converter, if used, should be disconnected from plug, and pilot light removed from its socket.

**A .25-megohm resistor is shunted across the i -f. transformer primary in the 1st detector plate circuit.

***A .25-megohm resistor is shunted across the i -f. transformer primary in the 1st i -f. tube plate circuit.

NOTE: All voltage -divider resistors and all resistors intended to produce a voltage drop are plus or minus 10%. All high -impedance circuit resistors, grid filters, etc., are plus or minus 20%.

'47 control grid to control grid 8,800

'47 control grid 129,400 '47 control grid to neon

lamp 554,400 '47 screen grid to '80 fil. 0

Large plate terminal of neon lamp 10,000

Rectifier filament winding .1 '80 anode to anode 166 '80 anode to speaker socket 186 Heater (2.5) .02

Following not to chassis: Output trans. pri. (total)

(Br. -Red -Br.) 850 Output trans. sec. .8 Large speaker field coil

(Blk: Gray) 850 Large speaker voice coil 8 Small speaker field coil

(Blk: Yellow) 650 Small speaker voice coil

(Br. -Green) 16.5 Between large speaker voice

coil and output trans. sec. 1

Across a -c. plug (105 v.) 1.8 Across a -c. plug (115 v.) 2.02

Attached to the aerial proper is the An- tenna Rejectostat, shown in Fig. 3. This should be mounted with the leads down to shelter them from rain. From this Rejec- tostat runs the lead-in wire, which in this case is referred to as a transmission line. It consists of two conductors in a shielded, insulated cable and it may be any length from practically nothing up to as much as 1,000 feet, without introducing the usual losses.

To the other end of the transmission line is connected the Receiver Rejectostat, which in turn is connected to the aerial and ground terminals in the receiver. This Rejectostat and the manner of making the connections is shown in Fig. 4.

Two other typical installations of the Re- jectostat System are shown in Fig. 5. In cases of this sort it is important to re- member that the usual window lead-in strip must not be used. The shielded transmission line must run intact directly to the terminals of the Receiver Rejectostat. Any break or discontinuance for a space of the shielding will undo the advantages of the system.

SPECIAL CONSIDERATIONS

Take note of the fact that there is a ground connection at the Antenna Rejecto- stat as well as the Receiver Rejectostat. Make each as good a ground as possible, prefera- bly a water pipe or a girder of the building, or in the case of a residential installation, a ground rod or plate if no water pipe is handy nearby.

Do not allow the transmission line to

Fig. 3. The Antenna Rejectostat. This should be mounted with leads down

to shelter them from rain

GROUND CLAMP

to hold braided wire sleevin9

TRANSMISSION LINE CABLE

to Receiver Rejectostat

ANTENNA LEAD

«GROUN.D LEAD to nearest good round

All connections to be

soldered and taped

AUGUST, 1932 199

GENERAL DATA-continued

hang from the Antenna Rejectostat. It should be tied off to several supports on the way down to the receiver.

The Receiver Rejectostat may be mounted anywhere within the cabinet of the receiver just so long as it is within the reach of the shielded antenna and ground leads from the

GROUND CLAMP to HOLD BRAIDED WIRE SLEEVING of TRANSMISSION LINE CABLE

SOLDERED

TRANSMISSION LINE CABLE from ANTENNA

REJECTOSTAT

Fig. 4. The Receiver Rejectostat. This unit is mounted in the receiver cabinet. Be sure the shield is replaced over the

aerial and ground leads

LEADS FROM RECEIVER

CHASSIS

FORCE SHIELD ',INTO HOLEw,th

TURNING MOTION

chassis. When connecting up these leads the cover plate of the Rejectostat must be removed. Be sure it is replaced after the connections are made. It is also necessary to ground the shielding of the transmission line at this point. A water pipe is preferable.

REJECTOSTAT EQUIPMENT

The Rejectostat Kit consists of one transmission line antenna impedance -matching

-transformer (Antenna Rejectostat) covering 550 to 1,900 kc., one transmission line receiver impedance -matching transformer (Re- ceiver Rejectostat) covering 550 to 1,900 kc., and three additional tube shields to be placed over the openings in the tops of the tube shields for the type 58 tubes. The

Fig. 5. Showiew two satisfactory methods of installing the system on an apartment house. An outside

antenna must be used

ANTENNA

i' ANTENNA j REJ TOSTAT 1- II:

TRANSMISSION LINE TO APARTMENT RADIO RECEIVER

REJECTOSTAT

ANTENNA ANTENNA REJEC O AT

11

TRANSM ISS ION LINE Out,rde or ln,rdr of buildin8

PTO RADIO RECEIVER REJECTOSTAT

V

positions for these extra shields are indicated by the arrows in the sketch of Fig. 1.

The transmission line may be No. 18 rubber covered copper, twisted pair, shielded with copper braid sleeve, and covered with 1/16" rubber covering.

A more detailed explanation of a similar noise -reducing transmission line system will be found elsewhere in this issue.

Resistance Data For Radiola 66 The following values of resistance of

some of the units used in the Radiola 66 may be of interest during point-to-point resistance measurement, or some other kind of similar test.

Antenna coil primary, 40 ohms. Second- ary, 5 ohms.

R -F, transformer primary, 44 ohms. Sec- ondary, 5 ohms.

First i -f. transformer primary, 20 ohms. Secondary, 100 ohms complete.

Second i -f. transformer primary, 20 ohms. Secondary, 100 ohms complete. The taps upon the i -f. transformer secondary windings are situated at the 50 -ohm point.

Third i -f. transformer primary, 20 ohms. Secondary, 100 ohms.

A -F. transformer primary, 1,050 ohms. Secondary, 5,000 ohms.

Power transformer plate winding, 240 ohms total.

First filter reactor (choke), 220 ohms. Second filter reactor (choke), 800 ohms. Output choke, 515 ohms. Speaker transformer primary, 1,485 ohms.

A -K Volume Controls The following are the reputed values of

volume controls employed in some A -K receivers. In contrast to the measured and known values of fixed resistances quoted elsewhere in this section, the values in this paragraph are compiled from sources believed to be accurate.

Models 37, 38, 39, 40, 41, 42, 43, 44, 45, 47, 52 and 53 use an antenna volume control rated at 500 ohms. (Courtesy, Cen- tralab )

Crosley Receivers The early 40-S, 41-S, 42-S models em-

ployed Type J speaker fields which required 85 milliamperes for excitation. Later models employed Type M, 45 -milliampere speaker with plug connections.

Early models had no pickup terminal; pickup connected directly to detector grid. Later models have pickup terminal. In some instances a choke and a .001-mfd. condenser are. in the pickup lead. Three types of volume controls used. Types 1 and 2 are similar except that in Type 2 the antenna resistor was shunted across the winding. In Type 3 no antenna shunt resistor was used.

Models 20, 21 and 22 were built for use with Type E Dynacones. When the Type C Dynacones with separately excited field were introduced, two terminals, Red and Black, were added to the chassis for sup- plying the current to the Type C field coil. The field coil is connected directly across the filament supply.

Fada Notes The Model 25 Fada receiver is available

in two productions. The early type employs the 180 electric unit. The later type employs the M 250 electric unit. The former production can be recognized by the fact that it employs two neutrodones. The later production has three neutrodones. One of these is the regeneration control. It is unneces- sary to remove the chassis to note the model. The neutrodones can be seen from the top when looking down upon the chassis.

Hidden Condenser Short A short time ago I ran into a peculiar

condition in a superheterodyne receiver that had me stumped for a while. All voltages were correct and yet the set would cut out at KDKA and above that point be dead.

This condition would ordinarily indicate shorted plates in one of the gang condensers, but they proved to be all right.

It finally came about that one of the set

An odd case: The set screw on the rotor shaft became loose and touched the stator section when about 15 de-

grees below the center, as shown

screws on the third condenser shaft had become loose and touched the stator, due to gravity, when it reached a position about 15 degrees below the center line, as shown in the accompanying sketch.

W. J. Gilliland.

Fada Speaker Fields Editor, SERVICE:

With reference to a paragraph concern- ing "Fada Speaker Fields" on page 167 of the July issue of SERVICE, it might interest you to know that there is no confusion in the identification of Fada speaker field coils as the first part of the article would indicate.

First of all, we wish to advise that there is a misprint in connection with the speaker used with the Model 66 Receiver. The speaker used on this model is a 12-B, not a 12-A, and it uses a 3 -1407 -Ms field coil.

With this exception the rest of the data is correct and should prove of value to a certain class of Service Men.

L. J. BELL, Service Manager, FADA RADIO AND ELECTRIC CORP.

200 SERVICE FOR

GENERAL DATA -continued

Clarion AC -280 and 25-280 The Clarion (Transformer Corporation of

America) Models AC -280 and 25-280 are both 12 -tube AVC superheterodynes, the first for 60 -cycle lines and the latter for 25- to 40 - cycle lines. The power consumption of both models is 129 watts at 115 volts.

The accompanying schematic diagram provides most of the necessary details. It should be noted that a pair of 27 tubes are used in a push-pull diode connection for de- tection and automatic volume control. Auto- matic volume control is obtained by the drop in voltage across the 25,000 -ohm resistor. The voltage drop is impressed on the grids of the r -f. and i -f. tubes.

9EOT/ON fl -H

VO/CECO/L 9r9Rr _n F- RED- FIELD CO/L O7ARr

' VÓ/CE CO/L FIN/91./

GREEN-F/ELO CO/L F/N/SH

VO/CE CO/L

F/ELO COIL

Color -coded connections to the G-1503, 400 -ohm field, dynamic speakers in the Clarion AC -280 and 25-280

receivers

Also note that four type 46 tubes, connected up as pentodes, are used in the power stage. They are paralleled in a push-pull circuit. These tubes can create noise and it will be found that a felt ring has been placed over the top of each one to prevent vibration and the possibility of one tube coming in contact with another.

Two dynamic speakers are used, the fields of which are connected in series and form a part of the filter system of the power - supply unit. Note that they are tied in the negative side of the filter system and create the necessary voltage drop for biasing the grids of the 46 tubes.

SERVICING

A voltage analysis is provided in Table 1. Readings are based on a line voltage of 115, and should be taken with the volume control at maximum and the muting switch "out."

A whistle similar to oscillation will be caused to appear on the sidebands of strong stations if the antenna is too long, due to overloading of the first detector tube, and should be remedied by inserting a .002-mfd. to .00025-mfd. condenser in series with the lead-in to the set, or by cutting down the physical dimensions of the aerial.

It might be well to add that general oscillation in the receiver may be caused by an open screen -grid bypass condenser, an open r -f. cathode bypass condenser, poor ground, or a high -resistance connection in series with

2 kc. of the exact center of the r -f. carrier. It is understood that this "channel con-

trol" circuit was developed in the labs. of the National Union Tube Co., and manufacturers reputed to be working with the idea

TABLE 1

Tube

R -F. lst Det.* I -F. Osc. Duo Dets. 1st A -F. Pwr. Tubes** Rect.

Fil. Plate Grid

2.2 250 2.3 242 2.2 249 2.2 110 2.2 0 2.3 237 3. 2.4 245 32. 4.9 340

.2

4. .2 .05

2.

Cath. Screen Plate M.A.

4. 77 4. 5. 85 .25 4. 77 2. 0 0 8. 5. - - 9.5 3.

3. 108

* Suppressor grid= --0 **Outer grids=245 volts

one of the above bypass condensers, or a dis- arrangement of wiring in the r -f. section of the chassis.

The adjustment of the trimmer condensers should be carried out in the usual manner: i.e., by the use of an external oscillator. The i -f. frequency employed in these two models is 175 kc., therefore the external oscillator should be set at 175 kc. and fed into the input of the receiver.

Lock -In System

Wurlitzer engineers compel owners of Lyric receivers to tune correctly by having instituted in the Lyric circuit a so-called "channel control system." This arrangement employs another tube, in addition to the AVC tube, whose purpose is to automat- ically prevent any signal coming through the receiver until the listener has tuned almost exactly to the carrier. Therefore, no such device as a tuning meter is necessary.

This extra tube gets an r -f. input through a very selective input but refuses to release hold of the following tubes, over which it has control, until this r -f. input is within

are Zenith, U. S. Radio and Television, Co- lonial and Echophone. So, tighten your belt and get ready for another queer circuit to test.

Adjusting Crosley Musicones It may appear strange in this day of dy-

namic speakers to give adjustment instructions covering old type magnetic units. However, a great deal of these units are in use and interest has been evidenced therein. These speakers must be readjusted when the plate voltage applied to the output tubes is changed. This applies to an increase or decrease. Use a long shank screw -driver. Connect the speaker to the receiver with which it is being operated. Tune to a station. Now turn the adjusting screw clockwise until the speaker chatters. Now turn the adjusting screw counterclockwise, counting the number of turns, until the speaker again chatters. Now turn the adjustment screw clockwise exactly one half the number of turns previously manipulated counterclockwise. The adjustment now is complete.

Schematic diagram of the Clarion AC -280. Note that four type '46 tubes are used as pentodes in a paralleled push-pull output circuit

R.F.-d/av3E /Jher-d7 /F. S/av31

r H H.

r NE CONTROL

lLV.C. OET. 9V0/O-S6POWER TUNING SHI,V re 2-27 HO. G \ 6 SW/Tc.Y

K

00/147S

/ MEO.

AOOnJMFO.

May.

J MFG

4J0Ma' 7S0/4, OLUME

,CONTROL

03C -P7 /MFO. I OM B,/OOA /OOO+L

ç. .

-,ppa _EhIFiC_

=

CM,R

< .RiMFLr .nlHln

RECT.-80..

1F.KR rL'ca.r.

AUGUST, 1932 201


New Fada Models The Fada "RA" series covers the Models

74, 76, 83, 87, 88 and 89 receivers. The "RE" series (detailed in this issue) covers Models 73 and 85 receivers. The "RC" series covers Models 78 and 79 receivers.

Atwater -Kent Chassis Specifications A certain amount of confusion may be

existent relative to the type chassis to be found in certain Atwater -Kent cabinet models of last year. The following are the complete models and the chasses employed:

Model 70 Lowboy: Used Chassis L for 60 -cycle a -c. service; F for 25 -cycle a -c. service; D for 110 volts d -c. service; Q for battery service.

Model 72 Superhet. Lowboy used Chassis H for 60 -cycle a -c. service.

Model 74 Table Model used Chassis L for 60 -cycle a -c. service; F for 25 -cycle a -c. service, and D for 110 -volt d -c. service.

Model 75 Phono -combination used Chas- sis P for 60 -cycle a -c. service.

Model 76 Highboy used Chassis L for 60 -cycle a -c. service; F for 25 -cycle a -c. service; D for 110 -volt d -c. service; Q for battery service.

Atwater -Kent Resistance Values The following tables provide the values

in ohms of all resistors in 24 distinct mod- of Atwater -Kent receivers. The

codings for the carbon type resistors are also included. The wire -wound resistors in the receivers listed are not color -coded.

TYPE 55-55C No. 14900 (With Transformer -Coupled R -F)

1 AF Cathode Bias .. 1,000 2 AF Filament Shunt 2 A F Filament Shunt (Total) 10 2 AF Bias No. 2.... 7,500 2 AF Bias No. 1.... 10,000 1 AF Plate Filter.... 30,000 Detector Cathode ....100,000 1 AF Grid Leak . .. .100,000 Detector Coupling... 50,000 Detector Plate Filter 50,000 Bleeder ... 6,500

or 5,000

RF Filament Shunt (Total) 10

TYPE D -I-16700

Detector Grid Leak 2 megs. Condenser Discharge 100,000 Screen Grid No. 2

Screen Grid No. 1

Detector Plate Filter 1 AF Filter Bleeder 3 RF Filament Shunt 2 RF Grid Bias 1 AF Grid Bias 3 RF Grid Bias 1 RF Grid Bias Filament Screen No. 2

Filament Screen No. 1

AF Filament Shunt

20,000 10,000 20,000

7,500 4,500

23 10 23 23 35

37-250 600 300

and 300

Yellow Maroon Gray Blue -Red Blue -Red Black Black All Purple

Purple Band

Green Blue -Red Black -Red Maroon Black -Red Yellow Blue -Green

TYPE D-2

Detector Grid Leak 2 megs. Condenser Discharge 100,000 Screen Grid No. 2 20,000 Screen Grid No. 1 10,000 Detector Plate Filter 20,000 1 AF Filter 7,500 Bleeder 4,500 3 RF Filament Shunt 23 2 RF Grid Bias 10 1 AF Grid Bias 23 3 RF Grid Bias 23 1 RF Grid Bias . 35 Filament Screen No. 2 37-250 Filament Screen No. 1 600 AF Filament Shunt 300

and 300

Green Blue -Red Black -Red Maroon Black -Red Yellow Blue -Green

TYPE F CHASSIS

2 AF Bias No. 1 50,000 2 AF Bias No. 2 30,000 1 AF Grid Leak 100,000 Detector Bias 30,000 Detector Coupling 50,000 Detector Plate Filter 30,000 1 AF Plate Filter 30,000 Detector Grid 2 megs. RF Bias Resistor 200 1st RF Bias 1,000 1st AF Bias 1,000 Bleeder No. 2 1,200 Dial Light 1 Yellow Filament Shunt (Total) 10 Bleeder No. 1 6,000 1 AF Grid Resistor 30,000 Gray

Black White Blue -Red White Black White Gray Green

TYPE L -I CHASSIS NO. 16,000

2 AF Bias No. 1 50,000 Black 2 AF Bias No. 2 30,000 White 1 AF Grid Leak ... 100,000 Blue -Red Detector Bias 30,000 White Detector Coupling 50,000 Black Detector Plate Filter 30,000 White 1 AF Plate Filter 30,000 Gray Detector Grid 2 megs. Green RF Bias Resistor 200 1st RF Bias 1,000 1st AF Bias 1,000 Bleeder No. 2 1,200 Dial Light 1 Yellow Filament Shunt (Total) 10 Bleeder No. 1 6,000

TYPE P CHASSIS

2 AF Bias No. 1 50,000 Black 2 AF Bias No. 2 30,000 White 1 AF Grid Leak 100,000 Blue -Red Detector Bias 30,000 White Detector Coupling 50,000 Black Detector Plate Filter 30,000 White 1 AF Plate Filter 30,000 Gray Detector Grid 2 megs. Green RF Bias Resistor 200 1st RF Bias 1,000 1st AF Bias 1,000 Bleeder No. 2 1,200 Dial Light 1 Yellow Filament Shunt (Total) 10 Bleeder No. 1 6,000

TYPE Q CHASSIS

Detector Plate Filter 30,000 Gray Detector Grid Leak..2 megs Green

Detector -AF Filament 1 Yellow lst-2nd RF Bias (Total) 22 3 RF Bias 20

TYPE H-1-(72 Chassis) (Below Serial 5,855,201)

IF Screen No. 1.... 50,000 Black IF Screen No. 2.... 20,000 Black -Red 1st Detector Bias .. 7,500 Yellow 1st Detector Screen.. 10,000 Maroon Oscillator Grid Leak 50,000 Black Oscillator Filter .... 10,000 Maroon 2 AF Bias No. 1.... 50,000 Black 2 AF Bias No. 2.... 30,000 White 1 AF Plate Filter.... 30,000 Gray 2 Detector Plate Filter 30,000 White 1 AF Grid Leak ... . 100,000 Blue -Red 2 Detector Coupling 50,000 Black 2 Detector Bias .... 30,000 White 1st IF Screen 10,000 Maroon 2 Detector Grid... 2 megs. Green 1 AF Bias 1,000 IF Bias 400 Filament Shunt (Total) 10 Dial Light 1

TYPE H-2-(72 )

(Above Serial 5,855,201) Dial Light 1

Filament Shunt (Total) 10 1 AF Bias 1,000 IF Bias 400 2 AF Bias No. 1 50,000 Black 2 AF Bias No. 2 30,000 White 1 AF Plate Filter 30,000 Gray 2 Detector Plate Filter 30,000 White Bleeder No. 2 10,000 Maroon 1 Detector Bias 7,500 Yellow Oscillator Grid Leak 30,000 White Oscillator Filter 10,000 Maroon 1 AF Grid Leak... 100,000 Blue -Red 2 Detector Coupling 50,000 Black 2 Detector Bias 30,000 White 2 IF Screen 10,000 Maroon Bleeder No. 1 20,000 Black -Red 2 Detector Grid... 2 megs. Green

TYPE 80-80F AND 83-83F Bleeder No. 3 15,000 Yellow -Gray 1 AF Grid Leak 1 meg. Blue -Gray 2 Detector Coupling 250,000 Red -Yellow 2 Detector Bias 30,000 Gray 2 Detector Screen 250,000 Yellow -Red Bleeder No. 1 6,000 Purple Bleeder No. 2 7,500 Yellow Oscillator Grid Leak 100,000 Red -Blue AF Bias No. 1 2 megs. Green AF Bias No. 2 500,000 Black -Purple Quality 10,000 Maroon 1 Detector Bias 2,000 Filament Shunt (Total) 10 Bleeder No. 4 100

TYPES 81 AUTO RADIO 1 AF Screen 10,000 Maroon Detector Grid 1 meg. Blue -Gray Control Grid Leak 1 meg. Blue -Gray Detector Bias 50,000 Black Quality 20,000 Red -Black Control Plate 800,000 Red -Gray Bleeder 1 meg. Blue -Gray

TYPES 82D -84D (Early 84D does not have resistor marked*) IF Bias 8 2 AF Filament Shunt 50

202 SERVICE FOR


Filament Series No. 1 60 and 170

Filament Series No. 2 35 Oscillator Grid Leak 50,000 i Detector Screen

No. 1 10,00 1 Detector Screen

No. 2 30,000 2 Detector Plate Filter 50,000 1 AF Grid Leak 250,000 2 Detector Coupling 100,000 *2 AF Grid 250,000 Quality 10,000

(Total 230)

Black

Maroon

White Black Yellow -Red Blue -Red Yellow -Red Maroon

TYPES 82 -82F -85-85F

(Some few early model 85 do not have automatic volume control. 85F made only

in late model.)

Bleeder No. 1 6,000 Bleeder No. 1 8,000 Bleeder No. 2 6,000 Bleeder No. 3 350 Bleeder No. 4 100 Bleeder No. 5 8,000 Bleeder No. 6 800 Bleeder No. 7 700 AF Bias No. 1 50,000 AF Bias No. 2 500,000 Filament Shunt (Total) 10 Filter Resistor 1,000

Oscillator Grid Leak.100,000 2 Detector Bias 30,000 Control Plate Resistor 800,000 2 Detector Coupling 250,000 2 Detector Plate Filter 50,000 AF Grid Leak 500,000 Quality Resistor 10,000 1 Detector t Screen 10,000 IF S

2 Detector Screen 100,000 IF Bias 1,000

TYPE 82Q

Filament Series Resis- tor No. 1 1

Bleeder No. 2 50,000 Bleeder No. 3 100,000 2 Detector Screen Re-

sistor No. 1 100,000 2 Detector Screen Re-

sistor No. 2 100,000 1 AF Plate Filter 50,000 2 Detector Plate Filter 30,000 2 Detector Coupling

Resistor 250,000 Bleeder No. 1 500,000 Quality Resistor 10,000 Oscillator Grid Leak.100,000

(85 early) (85F late)

Black Black -Purple

(not used in 82F and 85F) Blue -Red Gray Red -Gray Red -Yellow Black Purple -Black Maroon

Maroon

Blue -Red (85 early)

Black Red -Blue

Red -Blue

Red -Blue Black Gray

Red -Yellow Black -Purple Purple Red -Blue

TYPES 84-84F (Early Type)

1st Detector Bias 300 Oscillator Grid Leak 30,000 White IF Bias Resistor 1,000 Filament Shunt (Total) 10 Bleeder No. 1 6,000 Bleeder No. 2 6,000 Filter Resistor 1,000 (only in 84) AF Bias No. 1 50,000 Black AF Bias No. 2 500,000 Purple -Black 2 Detector Bias 20,000 Black -Red

2 Detector Screen Re- sistor 100,000

2 Detector Plate Filter 50,000 2 Detector Coupling

Resistor 250,000 AF Grid Leak 500,000 Quality Resistor 10,000

TYPES 84-84F (Late Type)

AF Bias No. 1 50,000 AF Bias No. 2 500,000 Filter Resistor 1,000 1 Detector Bias Resis-

tor 1,500 Filament Shunt (Total) 10 Bleeder No. 1 6,000 Bleeder No. 2 4,000 Bleeder No. 3 70 2 Detector Screen Re-

sistor 100,000 2 Detector Bias Resis-

tor 20,000 1 Audio Grid Leak 500,000 2 Detector Plate Filter 50,000 2 Detector Coupling

Resistor 250,000 Quality Resistor 10,000 Oscillator Grid Leak 100,000

TYPE 84Q Filament Series No. 1 1

Oscillator Grid Leak.100,000 Screen Resistor No. 1.100,000 Screen Resistor No. 2 30,000 2 Detector Coupling

Resistor 250,000 2 Detector Plate Filter 30,000 1 Audio Grid Leak 100,000 1 AF Coupling Resistor 50,000 2 Audio Grid Leak 500,000 Quality Resistor 10,000

TYPE 85Q Filament Series Resis-

tor 1

Oscillator Grid Leak 50,000 Local Distance Resis-

tor 10,000 2 IF Plate Resistor 100,000 2 Detector Screen Re-

sistor No. 1 100,000 2 Detector Screen Re-

sistor No. 2 30,000 2 Detector Coupling

Resistor 250,000 Bleeder No. 1 500,000 Bleeder No. 2 50,000 Bleeder No. 3 100,000 2 Detector Plate Filter 50,000 1 AF Plate Filter 50,000 Quality Resistor 10,000

Blue -Red Black

Red -Yellow Purple -Black Maroon

Black Purple -Black (84 only)

Blue -Red

Black -Red Black -Purple Black

Red -Yellow Maroon Blue -Red

Blue -Red Blue -Red Gray

Yellow -Red Gray Blue -Red Black Black -Purple Maroon

Black

Maroon Red -Blue

Red -Blue

Gray

Red -Yellow Black -Purple Black Red -Blue Black Black Maroon

TYPES 86-86F Filament Shunt Resis-

tor (Total) 10 Bleeder No. 1 8,000 Bleeder No. 2 6,000 Bleeder No. 3 1,000 Bleeder No. 4 400 Bleeder No. 5 8,000 Bleeder No. 6 800 Bleeder No. 7 700 Filter Resistor 1,000 (86 only) Dial Light Resistor 1

Oscillator Grid Leak .100,000 RF

1 Det tor Screen Resis-

IF .... 10,000

Control Tube Plate Resistor or

800,000 2 Detector Bias 30,000 2 Detector Screen Re-

sistor 100,000 2 Detector Plate Filter 50,000 2 Detector Coupling

Resistor 250,000 1 AF Grid Leak 500,000 Quality Resistor 10,000

Blue -Red

Maroon

( 250,000 Red -Yellow

J1 Red -Gray Gray

Blue -Red Black

Red -Yellow Black -Purple Maroon

86 ABOVE SERIAL 5,876,861 AND

86F ABOVE SERIAL 7,168,925

Bleeder Resistor 3A. 500 Bleeder Resistor No. 4 350

Filament Shunt 2 AF Bias Bleeder No. 1 6,000 Bleeder No. 2 6,000 Bleeder No. 3 100 Dial Light Resistor 1

Oscillator Grid Leak 1 Detector Bias Resis-

tor 2 Detector Grid Resis-

tor 2 megs. 2 Detector Bias Resis-

tor 50,000 2 Detector Coupling

Resistor 100,000 2 Detector Plate Filter 50,000 1 AF Grid Resistor 100,000 1 AF Grid Filter Resis-

tor 500,000 1 AF Bias Resistor 3,000 1 AF Plate Filter 30,000 Quality Resistor 10,000

TYPE 87

(Total) 10 200

50,000 Black

7,500 Yellow

Green

Black

Blue -Red Black Red -Blue

Black -Purple Green -Red Gray Maroon

87 ABOVE SERIAL 2,525,871 Bleeder 3A 400

TYPES 89-89F

AF Bias Resistor.... 200 Quality Resistor .... 10,000 Maroon Filament Shunt (Total) 10 Bleeder No. 1 8,000 Bleeder No. 2 8,000 Bleeder No. 3 2,000 Bleeder No. 4 400 Bleeder No. 5 8,000 Bleeder No. 6 800 Bleeder No. 7 4,000 Dial Light Resistor 1

Oscillator Grid Leak 100,000 Blue -Red Screen Resistor 20,000 Black -Red Control Plate Resistor 250,000 Yellow -Red 2 Detector Bias Resis-

tor 50,000 Black Control Grid Resistor 500,000 Black -Purple 2 Detector Coupling

Resistor 100,000 Blue -Red 2 Detector Plate Filter 50,000 Black 1 AF Grid Resistor 100,000 Red -Blue 1 AF Bias 3,000 Red -Green 1 AF Plate Filter 30,000 Gray

AUGUST, 1932 203

Public Address . .

"Class B" P -A. Amplifiers

Part II

The general criteria relating to the design of public-address systems, and the design information of Class B public-address amplifiers, have been described in the June and July issues of SERVICE. We will now proceed with the actual circuit design of such an amplifier, from which it will be comparatively simple for the reader to con- struct his own unit.

THE COMPLETE CIRCUIT

Fig. 1 is the circuit of the complete am- plifying unit. This amplifier has a gain of about 80 db. and an output power of about 20 watts. It must of course be realized that specific designs may depart from the circuit shown in several particulars to utilize available apparatus, or to meet specific problems. However, it is believed that the general arrangement shown will be typical, and suitable to most imposed conditions.

The circuit shown consists of three stages, the first a single 57 amplifier resistance -

coupled to a 46 driver, and the last a transformer -coupled Class B push -push stage, using two 46 tubes. The input transformer T-3 may be any good quality transformer designed for the particular circuit from which it is intended to operate. Suppose a double -button carbon microphone is to supply the amplifier. Then the transformer T-3 should have a turns ratio of 1 to 40 or 50. For single -button carbon microphones T-3 should have a turns ratio of about 1 to 65.

PUSH -PUSH TRANSFORMERS

The input and output push-pull transformers, for push -push operation, are special, and it should be understood that the usual type transformers cannot be used in these two positions. Thus, the transformer T-4 is of the step-down type and should have an impedance ratio (primary to one- half of secondary) of about 4 to 1. The output transformer T-5, on the other hand, should have a 1 to 1 ratio. A number of transformers of these types are now available.

It will be noticed that the suppressor grid

of the 57 tube is connected directly to the cathode. This is advisable to minimize noise (120 cycle hum or its harmonics) from the tube due to secondary emission from the screen. It is because of the increased hum due to screen emission that screen -grid tubes have never been particularly successful as preliminary stages in a -c. amplifiers. Such random effects cause both an increase in a -c. hum and in tube noise (so-called Schott Effect). The auxiliary grid when tied directly to the cathode effectively shields the plate circuit from such effects.

THE 57 AMPLIFIER

It is desirable to use the highest possible local impedance to realize as much gain as possible from this tube, which has an output impedance of about 2 megohms. If a choke coil is used to supply plate current (2 milliamperes in this case) it must have an inductance of at least 500 henrys to be effective. Since an inductance of 500 henrys has an equivalent reactance at 50 cycles of only about 150,000 ohms, it is evident that the plate impedance will be limited to this value, which is not sufficiently better than the 0.1-megohm resistor shown to warrant the expense. Moreover, due to the high distributed capacity of most chokes available for this service, they are likely to cause irregularities of considerable magnitude in the frequency characteristic of the amplifier in the useful frequency spectrum. In addition, they are subject to noise pickup from

The complete schematic diagram, with values and voltage data, for the Class B Public -Address Amplifier

/NPUr

150, 00O^ß t160V TIPPED POT. 241/1

13 Wire Wound

O.ln

Carbon

O.1n

1 -57

lu 1.0MFD

0. 5MF0.

-3V

-57 -46 FIL. F/LS

72 I

9

24110

*75V ..

2MFD

0.1MFD.

80.000- 80000". Carbon -J

-82

-46

1500- ^ Wire

Wound 30-

8MFD.

-33V

2MFD.

80,000.) ,<Carbon -l0 000-

i0, 000- air 8M10

*250V 20414

950V RMS

,00405?OQi 71 r

-46 T5

í400V 6MA-

200MA

4,000-

L1 L2 Wir eWouno

Ti T® MFD. I f3MFD

18MFD.

67 -mind Side of

OUTPUT

12,000"-' Wire Wound

110V -60ti a

204 SERVICE FOR

PUBLIC ADDRESS-continued

the rectifier (particularly where an 82 is being employed) or other circuit components due to their high impedance and such coup- lings may be extremely difficult to eliminate.

We believe that the above makes it quite clear why it is best to use a resistor. How- ever, even in the case of resistors, considerable care should be exercised in the choice of a resistor for this coupling since some units are apt to be noisy. A quiet composition unit, of molded carbon, is therefore recommended for both the 100,000 -ohm and 1-

megohm units. Since the 100,000 -ohm unit will carry a current of 2 milliamperes, the wattage dissipation will be about 0.4 watt. Therefore, it is well to use a unit rated at 1.0 watt. It is a good rule to use composition resistors at something less than half their rated wattage in all cases. The 0.1-mfd. condenser which forms a part of the coupling unit may be a paper condenser mounted in a non-metallic container. It should also be mounted as far as possible from the frame or other metal to insure low capacity to ground. A tubular condenser with wire terminals is excellent for this purpose.

THE POWER TRANSFORMERS

Two power transformers are shown in the diagram. The first supplies all filaments and the other the high voltage for the rectifier plates. Separate primary switches are shown. These are provided so that the filaments of the rectifier and amplifier tubes may be turned on some 45 seconds before the high voltage is applied. While this represents good design practice, it is not necessary to use separate transformers or to allow the filaments to heat up before the high voltage is applied.

The high -voltage transformer T-1 is also of special design and should have a resistance per side of about 150 ohms. The filament transformer T-2 must, of course, be able to supply the proper voltage and current for the filaments of all the tubes. Both types of transformers are now being mar- keted.

THE FILTERS

The chokes L-1 and L-2 each have a d -c.

resistance of about 200 ohms and an inductance of 12 to 25 henrys. These also are obtainable on the market, but in selecting chokes of this type make sure that they have a current rating of from 100 to 150 ma.

It will be noticed that 8-mfd. 500 -volt electrolytic condensers are specified for the power -supply filter. Either the wet or dry (Hic) type are satisfactory. Moreover, due to their high capacity, they are very effective in the prevention of motor -boating or low -frequency oscillation which is a source of considerable difficulty in high -gain, three - stage amplifiers. The best preventative for this type of trouble is sufficient low -frequency filtering. Choke coils are not particularly effective at frequencies of the order of a few cycles per second. Conse- quently it is good practice to employ resistance -capacity filters to obtain the neces-

sary degree of isolation between stages. This type of circuit is made more necessary due

AUGUST, 1932

to the fluctuation of the plate current of the push -push tubes. Thus, the voltage across the first filter condenser may vary as much as 50 volts during operation. This variable component which may be of the order of one or two cycles per second, must be filtered out of the plate, screen and control -grid supply of the first tube. For this reason the separate resistance -capacity filters for plate, screen and control grid have been employed. Since the change in screen voltage has considerably more effect on ampli- fication through equal changes in plate voltage, it is essential to filter this lead more completely than the plate. In some cases it may be necessary to increase the values of condensers at A and B to 8 mfd.

Due to the numerous high -resistance filters employed, it is obviously impossible to use a voltmeter for testing more than a few filter voltages. This is, therefore, an excellent example of a circuit that can only be properly analyzed by the resistance measurement method of servicing.

SPECIAL PRECAUTIONS

There are a number of precautions that should be taken in the design of this amplifier. They are as follows:

1. All tubes, in particular the 82, should have plenty of ventilation.

2. It is a wise precaution to mount all tubes vertically.

3. All condensers should be well removed from hot tubes or transformers.

4. The input transformer T-3 should be removed as far as possible from the rectifier circuit and should be rotated to the position of minimum pickup.

5. All grounds should be brought to one point and then tied to the ground wire.

6. All metal cases, cores, etc., should be separately tied to the ground wire.

7. None of the leads of the signal circuits should be cabled unless they have been by-passed outside the cable. Thus, as indicated in the diagram (1) , (2) , (3) and (4) may be cabled while (5), (6) and (7) should not be included in the cable.

8. The output impedance must always be equal to or greater than the load impedance for which the output transformer is designed. Otherwise the output tubes may draw exces- sive plate current and be destroyed.

The dotted lines in this diagram show the change in wiring necessary to make the Type 443 Mutual - Conductance Meter suitable for

measuring pentodes

9. All filament leads should be twisted. It is also good practice to run them in copper braid which is grounded.

LOUDSPEAKER CONSIDERATIONS

It is quite true that a Class B public- address system of this type may be used with the usual type of dynamic speaker the impedance of which varies considerably with frequency. It is best from the viewpoints of results and safety to both tubes and speaker, to use dynamic reproducers with substantially flat impedance characteristics. A number of manufacturers have placed upon the market speakers specifically designed for Class B work.

As to the number of speakers which may be employed, it would be best to re -read the article, "P -A. System Design" in the July issue of SERVICE. This article likewise covers the matter of impedance matching which is decidedly important.

Measuring Pentodes With G.R. Mutual -Conductance Meter

The Type 443 General Radio Mutual -Con- ductance Meter, developed several years ago for testing triodes, can be used equally well with four -element tubes. After a minor modification, both heater -type and filament - type pentodes can be measured.

The modified schematic diagram of the mutual -conductance meter is shown in Fig. 1. The dotted lines show the change in wiring necessary to make the Type 443 suitable for measuring pentodes. It will be seen that the cathode circuit has been broken and its two ends connected to two new binding posts. These posts are marked + and - Pentode. Screen.

For the measurement of the heater -type pentode tubes the two posts referred to above should be shorted, and battery connections are made as if a screen -grid tube were being measured.

The screen grid of a filament -type pentode is connected to the prong corresponding to the cathode of heater -type pentodes. Tests have shown the necessity for a source of voltage for the screen separate from that for the plate in the filament -type pentode, such as the '47. The connections for the screen grid are, therefore, made to the two new binding posts indicated in the diagram.

+ o --- PENTODE SCREEN

+LOW o

CURRENT

HIGH CURRENT } D-. 1.75A

4sß

BIAS PLATE + BATTERY_

I M.F.

PHONES

205

Short Waves .

Philco Models 4 and 4C

These two models are Short -Wave Con- verters, and differ only in the cabinets employed. It will be noted from the schematic diagram that the changing of wavebands is accomplished by a change in the capacities of adjustable condensers rather than a switching in and out of sets of coils.

The Converters are designed to operate on an intermediate -frequency of 1,000 kc., which means that the broadcast receiver with which the Converter is used should be tuned to 1,000 kc. Since there are broadcast stations operating on and near 1,000 kc., a trap circuit (17) is included in the antenna circuit to suppress interference.

vU

ttn_reR OCF T

RECTisIEQ emu

The frequency coverage for each switch position is given in the schematic diagram. A sketch of the underside of the chassis is also shown, with the location of each part designated.

SERVICING DATA

The tube socket readings are given in Table 1. These readings should be taken from the socket terminals, using a 1,000 - ohms -per -volt voltmeter. A set tester cannot be used either for voltage or plate current readings because of the effect of the long leads through the set tester cord.

Under no circumstances should any at- tempt be made to adjust the compensating

0

No. Description Part No. (1) Oscillator Coil 03733* (2) Bypass Condenser (.05 mfd.) 3615M 3 Gang Condenser 03692 4 Resistor (13,000 ohms) 3766

(5 Compensating Condenser (19 mc. end of top scale) 04000,E

(6) Compensating Condenser (8.5 mc. end of center scale) 04000,E

(7) Compensating Condenser (3.6 mc. end of bottom scale) 04000,E

(S Frequency Control Switch 03751 (93 Resistor (240,000 ohms) 3768

(10 Condenser (1250 mmfd) 5886 (11 Compensating Condenser (8.5 mc. end of top

scale) 04000F (12) Condenser (800 mmfd.) 5878 (13) Compensating Condenser (3.6 mc. end of center

scale) 04000F (14) Compensating Condenser (1.5 mc. end of bottom

scale) 04000F

Includes matched oscillator coil and detector transformer

osc toR.. ET ?CCK

`1)

CD 0

No. Description Part No. (15) Condenser (250 mmfd.) 3082 (16) Detector Transformer 03731 (17) Frequency Filter 03662 (18) Antenna Switch (plus 27) 5796 (19) Resistor (2 Megs.) 03879 (20) Condenser (110 mmfd.) 03879 (21) Condenser (250 mmfd.) 3082 (22) Resistor (99,000 ohms) 3767 (23) RF. Choke 03103 (24) Shielded Cable L4278 heard as the adjustment is being made. Be (25) Power Cord and Plug LA43A (26) Outlet Receptacle (27) On -Off Switch 5796 (28) Power Transformer (50,60 cycles) 5785

(2540 cycles) 5786 9) Electrolytic Condenser (6 mfd.) 4916 0) Electrolytic Condenser (6 mfd.) 4916

4951

í5,40

31)Filter Choke (50-60 2 cycles) 5930

(32) Tubular Resistor (9500 ohms; c. t.)

condensers in the field, unless proper equipment is available. The adjustment is extremely critical.

When adjustment is necessary use a modu- lated oscillator, accurately calibrated at 3,600 kc. (Should be electron -coupled or crystal - controlled type). The various harmonics and image frequencies of the oscillator signal are used to adjust the compensating condensers at the different short-wave dial settings. If the oscillator is off frequency, the harmonics and image frequencies will be off corres- pondingly.

For adjustment proceed as follows: Re- move Converter from its cabinet. Connect it to the broadcast receiver in the usual manner, with the ground wire connected and the aerial disconnected. It is important that the broadcast receiver be accurately calibrated at 1,000 kc. and that the dial be set exactly at this point.

For adjusting at 3.6 megacycles on lower scale, place the oscillator in operation and couple it with a wire to the antenna connection of the Converter. Be sure that the oscillator is grounded. Set the dial at 3.6 megacycles on the lower scale and set the frequency -control switch of the Converter in its proper position. Carefully adjust the "3.6 L" compensator, shown in the accompanying sketch, by means of a fibre wrench (Philco part 3164), until maximum signal

TABLE i

Tube

Det.* Osc.* Rect.

Plate Volts

25 110 (170 volts

Screen. Grid Cathode Volts Volts Volts

25 .3 0 - .1 0 on each plate)

*Filament voltage, 2.4.

is heard in the loudspeaker. It may be necessary to reduce the oscillator output by removing the oscillator from the coupling wire in order to obtain a faint input signal, the maximum strength of which can be read- ily determined by ear.

For adjusting at 1.6 megacycles, set the dial at 1.6 megacycles and adjust the "1.5" compensating condenser in the same manner as described above.

For adjusting at 7.2 megacycles, set the dial at 7.2 mc. and set the frequency -control switch in its proper position for the middle dial scale. Connect the oscillator output direct to the antenna terminal of the Conver- ter. Adjust the "8.5 M" compensating condenser for maximum output in the loudspeaker.

For adjusting at 3.6 mc. on middle scale, turn the dial to 3.6 mc. and adjust the "3.6 M" compensator.

For 18 megacycles, set the dial at 18 and the frequency -control switch in its corresponding position. Adjust the "19" compensator. More than one signal will be

...5439 sure to adjust for the one which is heard second as the compensating condenser capacity is reduced from its maximum (adjusting nut all the way in). When this adjustment has been made correctly, the oscillator signal can be heard at 18, 16, 14.4 and 12.4 megacycles. This adjustment is the most critical of any, and will require more care in getting the correct point.

206 SERVICE FOR

SHORT WAVES-continued

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SWITCH FREQUENCY PO5ITION (MEGACYCLES)

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Schematic diagram of the Philco 4 and 4C Short Wave Converter. The numbers in this diagram correspond to the numbers on the chassis and in the parts list on the

opposite page. The voltage data for the three tubes is given in Table 1

When adjusting at 8.8 mc., turn the dial to 8.8 and adjust the "8.5 H" compensating condenser in the same manner as described above.

In some cases it may be necessary to re- set the 1,000-kc. wavetrap (17) in the antenna circuit. If it is impossible to find a

point between 950 and 1,050 kc. at which interference is not heard, the wavetrap should be readjusted by means of the fibre wrench until the interfering station is tuned out.

Zenith Peak Frequencies Zenith Models 210-5, 211-5 and 270-5

Standard and Long Wave Receivers, with a

range of 200 to 2,100 meters, have an i -f. peak frequency of 125 kc.

Models 210 and 220, covering the range of 200 to 550 meters, have an i -f. peak frequency of 175 kc.

The Standard and Short Wave Models 250, 260 and 272 have an i -f. peak frequency of 175 kc. for the standard band and 1,000 kc. for the short-wave bands.

Noise -Reducing Aerials Transposition aerials (see June SERVICE)

and shielded transmission lines (see article in this issue) are being extensively employed for the reduction of man-made interference occurring in the broadcast bands. The same systems may also be employed for noise reducing on the short-wave bands, though a bit of revision is necessary.

The transposition aerial is employed com- mercially for short-wave reception, and generally consists of a single wire running in a straight line-or as near to a straight line as local conditions permit-and broken in the center. At this point an insulator is inserted, so that there exists two aerials rather than one.

Two leads are brought down to the receiver, one from each of the aerial wires, and these leads are spaced about a foot apart and transposed every 15 inches. That is, the two leads cross each other every 15

inches so that they are "continually out of phase." Square sheets of insulating material or insulating spacers are used at the points where the wires are transposed. The result is a sort of criss-crossed feed line.

This feed line, instead of connecting directly to the antenna and ground posts of the short-wave set, has a 400 -ohm resistor in series with each lead and the other terminals of the two resistors connect to a coil made up of about 5 turns of wire. This coil is coupled to the secondary coil of the antenna transformer in the short-wave set. No ground connection is used as a part of the antenna system.

This form of aerial is directional. Recep- tion will be maximum at right angles to the run of the aerial. Thus, if the aerial points north and south, the best reception will be from the east and the west.

(Arthur Lynch, Radio -Craft, Sept. 1932)

I -F. Interference' One of the major complaints heard here

in the East about short-wave converters, at least the early crop, is that broadcast -station interference upon the converter i -f. peak is very pronounced. In due justice to those units which are equipped with trap circuits tuned to the i -f. frequency, let it be said

This form of wave trap is satisfactory for the elimination of an interfering signal of broadcast frequency which falls on the i -f. frequency of the short- wave converter. The coil and condenser should be mounted in a shield

that the reason for the complaint is the absence of such a trap circuit.

Fortunately for all concerned, the circuit is assembled with little trouble and once ad- justed requires no further attention. The trouble is equally rampant with converters with i -f. peaks at either 1,000 kc., or there- abouts, or at 550 kc. With the broadcast receiver tuned smack on the nose to the 1,000 kc. signal, very little stray capacity in the converter is required to enable the passage of a 1,000-kc. signal from the aerial attached to the converter into the set, thus ruining all hope of listening without broadcast -station interference. This is particularly true if the station operating at the frequency employed is the intermediate frequency for the converter, and is nearby and powerful.

The circuit attached herewith illustrates the application of the filter which is arranged as a parallel resonant trap in the aerial circuit of the converter. The trap circuit finds application despite the provisions usually incorporated to allow changing of the converter i -f. peak over a range of perhaps 50 kc. either side of the rated intermediate. The following data is prepared for trap circuits to be tuned to any one of the frequencies named with a .00035-mfd. condenser, utilizing about 50 per cent of the capacity in the condenser. The frequencies are 1,500 kc., 1,100 kc., 1,000 kc., 650 kc. and 550 kc. The trap is located close to the converter antenna post and should be shielded. If desired, it can be connected within the converter, between the aerial post and the short-wave coil connection thereto. All forms are 2 inches in diameter and all coils are wound with No. 32 DCC wire. No spacing between turns. Approximate capacity to be used is .000175 mfd. Since the condenser is variable, the required adjustment may be made.

For 1,500 kc. use 36 turns. For 1,100 kc. use 45 turns. For 1,000 kc. use 49 turns. For 650 kc. use 91 turns. For 550 kc. use 111 turns.

To adjust the trap circuit, wire into circuit and set condenser to about half of maximum capacity. Now make the b.c. receiver most sensitive to intermediate frequency adjustment. Tune exactly to the short-wave i -f. frequency. Note the presence of the interfering station and readjust trap accurately until the station is tuned out. It must be understood that the trap circuit suggested is for the elimination of the broadcast station operating upon the short-wave converter intermediate frequency and not for short-wave stations which may interfere with other shortwave reception.

Socco! What this country needs is a good self -

healing milliammeter.

Ha Cha A broadcast listener phoned us and said

that his new 1933 set went on the blink and now he gets nothing but muting!

AUGUST, 1932 207

Au to-Ra dio Carter Genemotor Data

The Gehetnotor consists of a motor, which operates direct from the storage battery in the car, coupled to a d -c. generator. The generator feeds into a double filter (to the left of the motor -generator in the illustra- tion) which employs chokes and condensers.

Under most conditions the Genemotor draws less than 2 amperes from the storage battery, but this of course varies to a certain degree, depending on the milliampere drain of the auto radio receiver with: -which the Genemotor is used. With a receiver drain of 30 ma. the standard model Genemotor will draw 2.2 amps. from the storage battery with 180 volts output, and 1.7 amps. at 135 volts output. On other models of the Genemotor the storage battery drain is 1.94 amps. and 1.65 amps. respectively. The percent of regulation in practically all cases is 88%.

INSTALLATION

Genemotors 4680A and 4635A weigh 11 pounds and measure 41/2 by 61/2 by 6 inches. Genemotors 680A, 633A, and 6680 weigh 14 pounds and measure 5 by 53/4 by 91/2 inches. They may be mounted in any desirable location in the car-except in the engine compartment-but should be attached so that the motor -generator hangs down. The correct and incorrect ways of mounting are shown in the accompanying sketch. Figs. 1 and 2 of this sketch indicate the connections to the connector strip when the positive lead of the storage battery is grounded, and when the negative lead is grounded. The same sketch as referred to above also shows the complete connections for a typical installation job.

Since many auto radio sets were origin -

The Carter Genemotor. The double filter is in the case to the left of the

motor -generator

ally designed to operate on 135 volts "B," the set will naturally be more sensitive, and the noise level between stations will be more apparent, particularly on superheterodynes, if a 180 -volt Genemotor is used. Likewise, due to increased screen voltage, the set will tend to oscillate. In such a case, either use a 135 -volt Genemotor, or adjust the intermediate tap on the 180 -volt Genemotor to the proper voltage by alter- ing the position of the sliding contact on the voltage -divider resistor. Obviously, the same results can be obtained by increasing the values of the screen resistors in the set, if such resistors are used. And a resistor may be used in series with the 180 - volt tap and the receiver if this voltage must also be reduced.

Radio sets having only two "B" wires do not, of course, require an intermediate tap at the Genemotor, as the necessary voltage - reducing resistors are in the ,set. In such

Connection and installation details for the Carter Genemotor. Note in particular the terminal connections shown in Figs. 1 and 2

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cases merely disregard this tap, but do not remove the resistor. Sets having three "B" wires require the intermediate tap, which is set at the factory at 90 volts on the 180 - volt Genemotors and at 671/2 volts on the 135 -volt Genemotors. Usually these are the proper settings and should not be varied unless the set fails to operate properly. To change the intermediate voltage tap, loosen the screw that holds the contact on the resistance unit and move the contact to a position where the best results are had from the receiver. Then tighten the screw so that the contact cannot vary its position.

Janette Auto "B" Diagrams We have received word from the Janette

Manufacturing Company, 556 West Monroe Street, Chicago, that Service Men may obtain upon request diagrams showing the method of installation of the Janette Auto - B -Power on Majestic, Philco, Delco and At- water Kent auto radio sets.

There are two diagrams for each type of set, one showing method of installation where the negative car battery lead is grounded, and another showing installation where the positive car battery lead is grounded.

Diagrams covering other makes of auto radios will be issued shortly.

Reducing "C" Battery Voltages It is customary to reduce "B" battery

voltages by means of a series resistor. The voltage drop developed across the resistor reduces the voltage effective at the unit connected to the resistor, as for example the screen grid or plate of a tube. However, the same is not true in "C" bias circuits, for the simple reason that current does not flow in the circuit. Hence, there can be no voltage drop across the series resistor. The most effective method of reducing "C" bias voltages is to arrange "bucking" voltages. Thus, if a "C" voltage of about 16.5 volts is required and the battery available provides 22.5 volts, another 6 -volt "C" battery, with polarity reversed, can be connected in series with the 22.5 -volt lead and the final voltage will be 22.5 minus 6, or 16.5 volts. When arranging such bucking batteries, the minus lead of one is connected to the minus terminal of the other. The plus terminal of the bucking battery then becomes the minus terminal of the system. The final voltage is equal to the smaller voltage subtracted from the greater voltage and the polarity of the voltage supply is that of the greater voltage.

The opportunity for such a circuit arrangement may arise in connection with automobile and other types of battery-operated receivers.

Interference Helps Some Buick cars do not have the wind-

shield grounded. Grounding the windshield as well as the metal pieces at either end will be found helpful.

In Chevrolet cars, other than the latest models, it might be well to bond the rain spout to the chassis. Bonding at several points is preferable to a single point.

If you are confronted with the bonding of an aluminum plate, which under normal conditions cannot' be soldered, drill a small hole in the shield and rigidly attach a brass screw. You can then solder to the -screw.

208 SERVICE FOR

RADIO FANS WANT Results

YOU CAN GIVE them

SERVICE RESULTS with

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FREE HELPS Given with Initial Order

of First -Aid Kit

RADIO RESISTOR GUIDE Ready reference guide for servicing the most popular sets for resistor replacements.

OHM -DIAL Instantly tells the resistance value of any resistor according to the R. M. A. Color Code.

SERVICE LABELS For placing in back of sets to properly record the job and leave your own reminder -ad.

*,': ` w : at. . ' i'^:=n t._ ,. ^ -

-`',rJr': -"ea.,: ' =: # : ' - ; . .. ..A4r+ì* ..

t4-e.,

FOOTBALL and World's Series! Every radio fan agog! And, those sets that

have seen summers and winters of service are beginning to show the strain.

Resistor replacements are in order in

thousands of cases. Set owners rely on you for getting results and you must be sure of the parts that give results.

We've made everything simple, sure and profitable for the Service Man. "Protect -O- Packed" Resistors to keep wire -leads straight, resistance value and brand name stamped on each piece, publicity to popularize resistor importance - these, and many other features are back of OHIO HMS.

Write for prices and details

THE OHIO CARBON CO. 12508 Berea Road Cleveland, Ohio

OHIOHMS are made in Canada by C. C. Meredith & Co., Ltd., 67 Bay Street, Toronto

FIRST -AID KIT

Pocket size furnished in 1 -watt and 2 -watt types.

SPARK SUPPRESSOR SETS

For eliminating ignition interference on auto radios

AUGUST, 1932 SAY YOU SAW IT IN SERVICE 209

ON THE JOB... FIRST PRIZE

TONE QUALITY-SATISFIED CUSTOMERS

By A. M. Hayes

It has been our experience in the last few years of over -production, inflation and consequent failures of our business houses that even though it has brought about forced economies on the part of the receiving set owners, who are our largest number of customers, it has not decreased the desire for natural tone quality. With this fact as a basis to work on, we have been enabled to make a good many honest dollars by continually bringing it to the attention of our customers.

The sales field is unlimited for the Ser- vice Man along this line. We have found it to be composed of the owner who has a beautiful piece of cabinet work containing an obsolete receiver, having very poor selectivity and distorted tone; also the owner who has a receiver which is fairly modern but does not give the full timbre of tone which is so desirable.

It would seem that most receiver owners have adopted the attitude of "whatever your faults may be, I love you anyway," as far as his particular set is concerned. This attitude is formed because the cabinet fits into his home furnishings scheme in a particular spot or fashion, and because he has become used to its tuning and volume control peculiarities. It may be that when he bought the receiver it was perfection in tone quality, and his ear has become so accus- tomed to it, he still believes it to be perfect. This is the sales resistance which must be broken down, and it can only be done by direct appeal to his ears through the demonstration of a complete receiver of modern design, having perfect tone quality (as far as the ear can detect) or a demonstration of how his present receiver can be improved upon to bring it up to the present high standard.

Up to the present time there are only a few production receivers which, to our critical ears, can be used for a convincing demonstration of true tone, and we have adopted one in particular as our standard.

When we go out to make a complete receiver demonstration, we take the chassis of our adopted "standard" with its dynamic speaker fastened to a two -foot square baf- fle. The demonstration is made convincing by first playing the owner's set and then our "standard" set, calling his attention to lack of low tone and smoothness in his own set as compared to the "standard." In the majority of cases the difference is so great that there is no room for doubt on the owner's part as to the real beauty he has been missing in the radio programs. This generally results in the sale of the demonstration chassis and speaker with its installation in the owner's cabinet, giving him a modern receiver for well under a hundred dollars which cannot be surpassed in tone

ENTER THIS CONTEST Every month SERVICE awards prizes for the

three best merchandising, sales or manage- ment ideas used by Service Men to improve or increase their business. First Prize, $7.00. Second Prize, $5.00. Third Prize, $3.00. Your idea may win. Send it in now!

quality and performance by complete receivers costing three times as much.

For the owner who cannot afford a new set we demonstrate how his present receiver can be brought up-to-date at a slight cost. One demonstration in particular which has made many sales is due to the condition-especially in earlier receivers using two a -f. stages with a '27 in the first a -f. and a cathode bias resistor in this circuit- where there is inadequate bypassing of the bias resistor (mostly for the sake of econ- omy) and its failure to pass the lower frequencies. To demonstrate the failings of this condition we make an adapter to reach the cathode connection at the socket, and with the receiver operating we show the difference in tone by placing an 8 mfd. condenser in series between cathode and "B" negative.

This is only one of several demonstra- tions whereby tone improvements can be shown by proper bypassing, as the improp- er condition extends to all other circuits in many of the earlier receivers.

Another convincing demonstration can be made in tone improvement where a receiver has no r -f. choke in the detector plate lead. Our method of illustrating this is a plate - break adapter which cuts in an r -f. choke which is bypassed to cathode.

The wide-awake Service Man can always keep busy and make money if he will adopt an honest policy in his servicing and sales, and push tone quality in receivers.

SECOND PRIZE PROFITS IN NEW AUDIO CHAN-

NELS By C. L. Fairchild

I have arranged a portable audio system with dynamic speaker with the highest possible tone quality with the connections made so that it is possible to tap in at the output of the detector or first audio tube of any type receiver.

ABOUT COGNOVIT NOTES We are indebted to Mr. R. W. Cutts, of

Bloomington, Indiana, for his advice that Cognovit Notes are taboo in his State. Their use constitutes a misdemeanor punishable by a fine of $50 to $500 and/or imprisonment from one to six months.

Similar laws may hold in other States. Therefore, if you have any idea of using a Cognovit Note on your bills, check up on the local laws first.

Whenever I am able to sell a customer on the idea of a real tone demonstration- and this is not at all difficult-I hook in the portable amplifier and "show up" the customer's set.

As soon as I feel that the customer has recognized the vast difference in tone, I ex- plain to him that tone is largely determined by the type and quality of audio units used in a set. I finally get around to quoting him a price on a job which will make his set sound like the demonstrator. Usually just a change of a -f. transformers, or the use of larger tubes does the trick.

I have successfully closed alteration jobs running as high as $35 and these jobs have turned out to be the best form of business - getting for me, as the owner is bound to boast to his neighbors about the tone of his improved set.

I range these jobs from $12.50 up, according to what I have to install, and if times were normal I could keep one man busy on this work alone.

THIRD PRIZE FORM A CLUB By W. O. Barnet

Some time ago I decided that if I could gain the confidence of a group of young men it would greatly assist me in furthering my servicing business with the older people. This decision of mine was based on the time -worn, but truthful, saying, "What my son says goes."

Consequently, I started off with the names of about 15 energetic young men of high school age whom I knew to be interested in radio. To each of these young men went a letter, cordially inviting them to attend a ten -week session of one night a week, of radio classes. Everything free, of course.

The response was very good, and at the first meeting I saw to it that each young man became well acquainted with the others. The whole thing was handled just like the usual kind of radio club.

At each of these weekly sessions I gave them a lecture on radio, starting off with elementary electricity, and explaining everything in language they could understand. I had them ask questions, too, and they learned rapidly.

This little radio club idea has worked out splendidly, and I am starting my fifth class this coming October. The young men have not only transmitted their confidence in me as a "technical radio man" to their fathers but have advertised me outside their homes as well.

Five Years Hence The High Vacuum Tube Company has

just issued its latest 1,000 -page catalog listing the various tubes manufactured by said company. The first five pages are given over to an explanation of how to find the tube you are looking for. Included in the catalog is the latest 20 -pin tube, type 56789 -A -TZ -219, which beats as it sweeps as it cleans.

210 SERVICE FOR

MaelelevATNIZI .ANc. EXACT - DUPLICATE

For all makes

and models or Radio ...

The following is a partial list -of guaranteed Stancor EXACT - DUPLICATE Replacement Transformers, available for prompt

shipment from stock.

ALL-AMERICAN MOHAWK Models -Lyric 90, (25 cycle); Lyric 90, Lyric D & H.

APEX Models (superheterodyne) 10, 20, 36, 37.

ATWATER-KENT Models 37, 38, 55, 55-C, (late model) 55, 55-C; (early models) 60, 60-C, H-1, H-2, L-1, L-2, 82, 85, 82-F, 85-F; (early and late type) 84-F, 80, 83, 80-F, 83-F, 87, 89, 89-P, 89-F, 66.

BOSCH Models 29, 825.

BELMONT Models 41, 41-A, 47, 50, 51, 51-A, 51-B, 70, 71. (25 cycle) 42, 42-A, 48, 72.

BRUNSWICK Models (60 cycle) 14, 21, 81, 82, S-14, S-21, S-81, S-82; (Chassis D) 12, 12-A 16, 16-A, 18, 18-A, 33, 33-A, 10; (25 cycles) 14, 21, 81, 82, S-14, S-21, S-81, S-82; 2KR0, 3KRO, 3KR6, 5KR, 5KRO, 5KR06.

COLUMBIA Model SG -8.

CROSLEY Models (Chassis 73) 40-S, 41-S, 42-S, 82-S.

EARL Models 31, 32, 32-S, 41.

EDISON Models (Chassis JR and JC) R1, R2, C2.

EVEREADY Models -Series 30, 40, 50.

FREED Models 65, 78, 79, 79-S, 90, 95.

FREED-EISEMANN Model NR -85.

FRESHMAN Models Q15, Q16, 3Q15, 3Q16, QD16S.

GENERAL ELECTRIC Models H-31, 51, 71, T41C.

GENERAL MOTORS Model Chassis S9A.

GRAYBAR Models 310, 311, 700, 770, 900.

KELLOG Models 523, 526.

KENNEDY Models 10, 20.

KOLSTER-BRANDES Models K20, 22, 25, 27, 37, 24, 36, 43, B15, 16.

KOLSTER-COLUMBIA Model 950.

MAJESTIC Models 90, 9P6, 180, 8P6; (plate) 70, 7P6; (filament) 70, 7P6; (plate) 180, 8P6; (filament) 50, 15-A, 90-B, 100-B. Chassis 20 unmounted 21, 22, 23, 130-A, 230-A. Unmounted 25, 25-B.

PHILCO Models 20, 65, 76, 77,'::82, 86, 87, 95, 96, 296, 11, 211. For 245 tubes 112, 212. Using 247 tubes 112, 212. 70, 270; (60 cycle) 511, 521, 531, 541, 551 561 571; 511-A 521-A 531-A, 541-A, 551-A, 561-A, 571-A, 581-A.

TO service engineers this means that through their distributors, they may secure EXACT - DUPLICATE Replacement Transformers for all makes and models of sets ... one reliable source of supply ... assurance of the same exacting precision methods that have made Stancor transformers preferred for original equipment. No re -drilling, re -wiring or re -building the set to secure original balance and performance .. .

make a decent profit and wholly satisfy their customers.

Mail the coupon now, while it's in your mind and get catalog bulletin with price schedule and name of distributor nearest you.

RCA RADIOLA Models 80, 82, 86, 60, 62, 44, 46, 47; (60 cycle) 18, 17, 33, 51, 64, 67, 66, 48; (25 cycle) 42, 48.

RCA -VICTOR Models R-32, R-52, R-35, R-39, RE -37, RE -45, R-75, 7-11, 7-25, 9-18, 9-54; (25 cycle) R-15.

SILVER -MARSHALL Model Sheridan 750.

SPARTON Models 931, 589, 89-A, 301, 410, 420, 25, 26, 26-AW.

STEINITE Models 40, 59, 102, 40-C, 41-C, 60-C, 102-C.

STEWART-WARNER Models (Series A & B 60 cycles) 801, 801-A; (Series A & B 25 cycles) 811, 811-A.

STROMBERG-CARLSON Models 641, 642, 652, 654, 846, 848, 10, 11.

TEMPLE Models 8-60, 8-80, 8-90, 8-61, 8-81, 8-96.

UNITED AIR CLEANER Models 108, 108-A, 110, Sentinel 104.

TRAV-LER Model B.

WESTINGHOUSE Models WR -4, 5, 6, 7; (25 cycle) WR -4.

ZENITH Models 50, 60, 70, 10, 11, 12.

S T A N DAR D TRANSFORMER CORPORATION 862 BLACKHAWK STREET CHICAGO, ILL.

STANDARD TRANSFORMER CORP., Dayton & Blackhawk Sts., Chicago, Ill. Gentlemen:

Send me by return mail your Catalog of Exact -Duplicate Replacement Transformers together with price schedule and name of Distributor nearest me.

Name Address Firm and Position


THE FORUM... About "Two -Speaker Sets" Editor, SERVICE:

I have read with interest in the June issue of SERVICE the abstract on page 132 entitled "Two -Speaker Sets."

It appears to me that a person not well versed in the science of acoustics might easily assume from this abstract that the 3 db. increase in efficiency, due to the use of two loud speakers, extended over the entire frequency range. As a matter of fact, in the original article dealing with this matter (Wolff, Physical Review, June, 1929), it was shown that the theoretical gain to be expected from two 8" diaphragms, in contact, over one such diaphragm, was zero above 350 cycles. Measurements that we have made in this laboratòry have indicated that the gain extended somewhat above this frequency, possibly to 700 or 800 cycles, for reasons which we have as yet been unable to determine. We have quite positively concluded, however, that there is no gain above 700 or 800 cycles.

The Electronics' article appears to have been condensed for publication from a longer original paper. It seems probable that this and the further abbreviation occurring in your abstract would tend to omit some qualifying statements that would safeguard the reader against the idea that the efficiency may invariably be doubled over the entire frequency range by the use of an additional loud speaker.

The last paragraph in the abstract is, I believe, incorrect as it stands, because there is a flow of air from one speaker to the other, only in cases where the diaphragms are out -of -phase or where they differ greatly in size.

BENJ. OLNEY, Acoustical Engineer, STROMBERG-CARLSON TEL. MFG. CO.

Charges and Profit Editor, SERVICE:

We have been asked the question, "What is a Rightful Service Charge?" One man replies that his charge is only one dollar per hour and seems to infer that he cannot charge more because the plumbers and brick- layers in his town only charge that much. He admits that the plumber charges for time to and from the shop yet says that, personally, he does not. Why? Is not his time as valuable to his clients as is the plumbers' time?

I'll bet that every Service Technician worthy of his name is occupied with the problem of the probable defect in his client's radio from the moment he receives the call until the defect is eliminated, for certainly, when receiving the call, he will make in- quiry as to the make and model, and whether or not the radio is only weak, or noisy, or stone dead.

Does the plumber do as much? Perhaps he does-but even if he did not, he would still be entitled to remuneration for time spent in preparation for making the repair,

which includes traveling to the place where repair is needed. And, having completed the repair, he cannot well afford to aban- don his bag of tools, but must return them to his base of supplies for use on subse- quent calls.

Radio servicing, having become a highly technical profession, requires that the Ser- vice Man who would keep abreast with his profession, to study and experiment con- stantly, buy or build the most advanced servicing equipment, provide himself with complete sets of circuit diagrams and service information on all makes and models of radios, and maintain a fairly complete stock of tubes and replacement parts for the more commonly used models, which always includes the latest.

In addition to the technical part of the profession are the business and ethical parts. These latter, consisting of the bookkeeping in connection with the records of repairs and other services, the computation of charges and the collection of accounts, the records of cost in materials and time, and the professional ethics involving personal contact with customers, and relations with brother Ser- vice Men, manufacturers and dealers, also consume time and require constant study and revision to meet the needs of the growing art.

Therefore, the Service Man who would give honest and efficient service to his clients must first invest considerable in thought, in time and in equipment and supplies. Ex- perience is a valuable and absolutely necessary asset. It costs him money to render service, and it costs him more to keep prepared for rendering service. It has already cost him much to acquire his experience.

If, after making all of these expenditures, of time in patient study, for parts and accessories with which to experiment, for text books, trade periodicals, and expensive tools and servicing instruments, he has fitted himself for the job of making that sick radio sing again, is he not entitled to a professional fee for his services on a par with a doctor's fee?

Even though the patient is incurable, as he sometimes is, the doctor has used his well-earned knowledge and skill in an honest effort to effect a cure. So, also, has the Service Technician used his equally well- earned knowledge and skill in an effort to correctly diagnose and eliminate the defect in the radio.

It has been said that the Service Man sells time and knowledge, and that these are his stock in trade. His services are entirely professional and his one purpose is to get the radio working as it did originally. To accomplish this is sometimes only a few minutes work after he has arrived on location. Sometimes it takes several hours.

No standard scale of prices for his services has ever been set, nor can be set to adequately fit the individual call. In many cases the repair bill, if computed at a flat rate per hour, would be greater than the value of the radio repaired.

However, it is fast becoming standard practice to set a flat rate per hour upon all calls, plus the list price of materials and parts used, the minimum rate being for one hour, and the time being computed from the time of departure from the shop until re- turning thereto. The rate per hour actually charged seems to vary between $1.50 and $2.50 in the majority of reports, ap- pearing in the trade papers, which have been noticed by the writer.

Upon entering the profession of radio servicing, a little less than three years ago, the writer decided that one dollar per call, plus fifty cents an hour for more than one hour, was about all that his clients could stand. At the end of the first year he found he had cleared the magnificent sum of $13.97 over and above the cost of equipment, and not counting the sum of $13.25 in unpaid customer accounts. So he raised the ante to a flat rate of $1.00 per hour and, at the end of the second year, had cleared the tidy for- tune of $109.38, not counting unpaid customers' accounts totaling $40.15.

By this time several of his customers had new radios with pentode tubes and various other troubles, including oscillators and automatic volume controls. New test equipment was absolutely necessary. So he in- vested an even $300 more and shoved up his rates to $1.50 per hour, plus materials, and with a minimum charge of $2.00 per call.

After the first nine months of the third year he finds that he still owes $133 for his test equipment, and that he "is owed $118.65 on outstanding customer accounts. He hopes to have his "budget balanced" by the end of the third year, but is becoming a little skeptical. With six -prong tubes at hand and seven-prongers promised for the near future, it looks as though the only fellow who can profit at radio servicing is the manufacturer of servicing equipment.

The writer's guess is that if we Service Technicians are to stay in the profession, and if we desire to elevate and maintain the profession at a standard above that of a plumber or bricklayer, we may have to charge as much as $5.00 a visit, or else refuse to answer calls on radios which are equipped with tubes having more than sev- enteen grids per tube and three or four automatic volume controls.

At the same time the writer acknowl- edges the fact that multiple grid tubes, re- fined methods of volume control and noise suppression, with their attendant and more or less complicated circuits, will do much to raise the standards of the servicing profession by eliminating the quacks and cut- rates from the field, and by making it absolutely essential that the Service Technician, so-called, be that in fact and not merely in name. He is bound to answer many calls where the substitution of new tubes will not make. the radio play any the better nor satisfy the client.

M. K. BARBER, Fort Ethan Allen, Vermont.

212 SERVICE FOR

L _ Servicln9 Receivers

by means oi-

1R''esisance IVleasuremenl- - r 6

I

PUN F. RIDER

SAVE HOURS OF NEEDLESS WORK

SERVICING RECEIVERS

BY MEANS OF

RESISTANCE

MEASUREMENT

Resistance measurement is the modern way to service a receiver. It represents the ultimate test -so why shouldn't it be the BASIS for servicing operations?

Servicing Receivers by means of Resistance Measurement fully explains this method-shows how to get the most out of an ohmmeter and how to diagnose the trouble with the greatest speed and accuracy. Shows how all receivers, irre- spective of the circuit, are reduced to the same servicing level. In an emergency, this method allows you to work without the wiring diagram. To keep up-to-date, you simply must have this fine book. 203 pages; type set; cloth bound; well illustrated. Price $1.00 post paid. Sold with a money back guarantee.

RADIO TREATISE CO. 1440 Broadway New York, N. Y.

FREE UST the thing every service man needs! Easy to carry! -

and provides ample space for tools, small parts, 20 assorted tubes, a coil of wire, literature, etc. This kit is sturdily constructed, handsomely finished. It's planned by radio experts for radio experts! Speeds up work, impresses customers with your neatness, efficiency and professional standards.

Get the Sylvania Service Kit FREE! All you do is send us your purchase order for 75 assorted Sylvania tubes-any 75

se MODE

and a MONEY-MAKER for the SERVICE MAN

AMPERITE is the only self-regulating line voltage control that successfully com-

pensates for line voltage variations, up and down. Greatly improves reception and adds life to tubes and filter equipment. AMPERITE can be installed in any radio in five minutes. It is so easy to sell that service men are averaging from $60 to $110 extra profit each month.

R. Gordon, service man at 2504 Olinville Ave., New York, averages more than 40 AMPERITE sales a month. S. Commadore, 200 E. 104th St., New York, sells 60.

Get in on this live -wire money-maker. Those extra dollars are worth having.

4MPERITE (jrpo, euon 561 Broadway, New York

:::.; >;:-: ,,.,.. ,,.. m.

EE u8 OL

Send $1.62 to Dept. S-8 for dealers' sam- ple and sales helps.

Brass -Fitted, Leatherette -Covered

SERVICE KIT you want-to be billed through your regular jobber. You will receive your Free Sylvania Serv- ice Kit at once.

If you want-order 25 tubes at a time-when you've placed 3 such orders you will receive your kit!

Your customers know that Syl- vania tubes have been "tested for a set like yours." When you use Sylvania tubes steady consistent newspaper and radio advertising helps you make quick easy sales!

THE SET -TESTED TUBE

6 IMPORTANT FEATURES

1. Convenient Too Tray-plenty of room for aerial wire, etc.

2. Heavy Brass Fin- ished Lock.

3. Finished in Black Leatherette.

4. Elastic Straps for Advertising Material.

5. Capacity up to 20 Tubes.

6. Rugged Construc- tion, Professional Ap- pearance, Large Capac- ity.

Hygrade Sylvania Corporation, Sylvania Division, Date Emporium, Penna.

We are anxious to have a Sylvania Service Kit, and attach our purchase order for 75 25 assorted Sylvania Radio Tubes to be billed through

Jobber's Name Address

Name Signed

Address


THE MANUFACTURERS... Oak All -Wave Switch

The Oak Manufacturing Company of Chi- cago have announced a particularly worthy wave -changing switch for short-wave receivers and converters. This switch is minus many of the disturbing inadequacies of numerous switches of this type and seems to have had placed upon it a generous amount of engineering study before the final design was reached.

One of the features may be referred to as "noiseless switching." However, this phrase does not exactly cover the situation, as the switch is equally as noiseless when in a state of rest. This suggests an absence of any high -resistance contacts. This is accomplished by the utilization of silver-plated contacts of such shape and design that they bite into the surface of the contact rotor, removing all foreign particles (such as good old household dust) from the contacting surfaces and providing a connection reputed to have a resistance below one -thou- sandth of an ohm.

A simple stopping mechanism is provided which brings the switch to a very definite stop at the position of contact and yet allows the knob to be easily turned to the

next contact. This stopping mechanism is not a part of the functioning of the contacts, but rather is a separate unit.

The switch is so constructed that any con- ceivable switching circuit can be embodied with a minimum number of sections, and hence a minimum cost. As many as three poles can be placed on one rotor.

The dimensions of this switch are 1-3/4" by 2-5/16" and it can be mounted below a 2 -inch chassis using a single 3/8" mounting hole. A keying pin to prevent the switch from turning is also included. Length depends upon the number of switching sections required. The mechanical construction is sturdy and has the following features: Steel end -plates, 1/4" steel shaft, heavy brass side supports, brass bearings and silver- plated phosphor bronze contact clips. The stationary contacts are assembled on high grade bakelite insulation.

All -Purpose Power Amplifier The new Model 17 Combination Power

Amplifier Unit, just announced by the Op- eradio Manufacturing Company of St. Charles, Illinois, has a characteristic design of its own

that allows plenty of flexibility in application.

Nearly every sound application-including airport, sound truck, amusement park and dance hall installations requiring up to 15 watts undistorted output-may be filled by this unit. An additional output stage may be had to boost the output up to 30 watts.

The control panel of the amplifier has pro- vision for microphone, radio and phonograph inputs. Operating switches and volume controls for each input, an amplifier tone control, and all input connections are segre- gated on this separate unit that may be removed from the amplifier housing when remote control operation is desired. Exten- sion cables up to 500 feet in length may be used without affecting the operation of the amplifier.

The amplifier and control box are normally mounted in a crystalac-finished metal case provided with carrying handles and snap cover fasteners. Ample ventilating provisions are made. The amplifier may be slipped out of the end of the case for inspection. Knock-out holes in the case provide for conduit wiring.

New Tapped Bradleyometer A new tapped Bradleyometer is announced

by the Allen-Bradley Company of Milwau- kee, Wis., which provides automatic tone correction with volume control. It is well known that the sound pressure representing the threshold of audibility varies greatly with the frequency and is a great deal higher at low and high frequencies than in the middle register. Therefore a type of volume control is necessary which varies the frequency characteristics of the audio amplifier so that the apparent quality of repro-

'N0'IiiÍU+l1(iill(ìlQ?ÍD8'111='j'II

duction remains the same for all volume control settings. The new tapped Bradley- ometer achieves this result in any one of several audio -frequency networks and auto- matically accomplishes tone correction with volume changes.

The resistance element of the tapped Bradleyometer consists of 50 individual resistance steps molded in disc form and stacked alternately between metal discs of somewhat larger diameter. The contact arm makes contact along the edges of the large metal discs, and therefore the resistance units are not subjected to mechanical wear. A special tap on the resistance element is brought out to a fourth terminal. The network necessary to provide tone correction is usually connected between this tap and the grounded or low -potential end of the resistance element.

This new tapped Bradleyometer can be built up to provide any resistance -rotation curve, and in some designs each of the 50 steps may be different from the others. Con- trols can be provided with a logarithmic resistance -rotation curve to provide uniform decibel increments with knob rotation.

I.R.C. Power Wire Wound Resistors A new line of Power Wire Wound Re-

sistors has been introduced by the Interna- tional Resistance Company for the Engineer and Service Man. These resistors are made in 3 -watt and 5 -watt sizes, and within the next few months there will be units made up to 100 watts in steps of 10, 15, 25, 50 and 75 -watt sizes.

Particular attention, however, is being

Both the 3 -watt and 5 -watt I.R.C. resistors are made in this form, and differ

only in size

called to the 3 -watt and 5 -watt sizes at the present time. Both types have pigtails for ease in mounting, similar to the Metalized line of I.R.C. resistors.

The 3 -watt resistor is made in ranges up to 5,000 ohms and the 5 -watt resistor is made in ranges up to 15,000 ohms. These units were designed to meet the demand for a smaller resistor capable of dissipating high wattage. The 3 -watt resistor is about the same size as the /-watt Metalized resistor, and the 5 -watt resistor is about the same size as the 1 -watt Metalized resistor.

414 SERVICE FOR

Everything you need

to service resistor troubles-at a profit

Continental Resistor

Replacement Kit

Continental

THE new Continental Resistor Kit has taken every bit of uncertainty and confusion from the repair of

resistor troubles. You need every one of these helps to increase your profits from resistor repairs:

(1) Twenty-five Continental "Certi- fied" resistors in a small handy size steel kit in the most used values to provide immediate replacements.

(2) The Resistor Combination Chart which shows graphically and without cal- culation how to combine standard resistors in parallel to form unusual values frequently needed.

(3) R.M.A. Color Code Selector to obtain instant identification of resistors by color marking.

(4) The new Continental Replacement Resistor Guide (now on the press) to specify exact replacements for all receivers, old and new.

This kit, complete with all above items is a remarkable offer. Get yours today, and start making money on resistor repairs. Use the convenient coupon at the bottom of the page.

Continental Resistor Kit- Net to Servicémen $3.50

"Certified" Suppressors

Spark Plug Suppressor Type S8

ryLONTIN ENTAI.

Distributor Suppressor Type T9

Screw in Cable Suppressor Type Cl 0

USED by practically every large manufacturer of motor car radio sets, and recommended

by leading motor car manufacturers, Continental Certified Suppressors likewise find equal favor with the serviceman.

Ease of installation, ability to withstand heat and vibration, and absolute elimination of noise from spark plug and distributor discharges are assured when you demand the gen- uine Continental Certified Suppressor.

Three convenient types are provided. Type S8 for spark plugs, Type T9 for Distributor lead, and Type C10 that screws into the ends of a cut ignition cable. This last

type is very popular for use where space does not permit the use of the standard types. Supplied singly and in kits for 4, 6, 8, and 12 cylinder motors. List price, Continental Suppressors Types S8, T9 and C10..$0.50

CONTINENTAL CARBON Inc.

Use this coupon or write your jobber

Continental Carbon, Inc. 13900 Lorain Ave., Cleveland, O.

Canadian Plant, Toronto, Ont.

Gentlemen: Please ship C.O.D., one Continental Resistor Kit, com-

plete with R.M.A. Color Code, Resistor Combination Chart and card entitling me to the new Continental Replacement Resistor Guide.

Name

Address

My Jobber is

elg'"A Weston Single Meter ANALYZER

Weston Model 660

Every necessary socket voltage and current measurement, both A. C. and D. C., can be made on all modern receivers with this remarkable Weston Single Meter Analyzer.

Point-to-point tests are provided for with three resistance and ample voltage and current measuring ranges, available' at pin -jacks on the panel. Full description is contained in the new Weston -Jewell catalog.

Pattern 675 Tube -Checker

A new, low-priced instrument that checks all present types of tubes without the use of adapters. Six- teen tube sockets are ingeniously arranged to occupy small space. Test limits for all tubes are etched on the instrument panel. Write for the Weston -Jewell catalog describ- ing this great instrument value I

WEBTON JEWELL

Weston Electrical Instrument Corp. 604 Frelinghuysen Ave. Jewell Electrical Instrument Co. Newark, N. J.

Please send me a copy o !your new catalog listing the complete Weston -Jewell line of radio instruments.

Name

Address City


THE MANUFACTURERS-continued

Continental Replacement Kit A new resistance replacement kit has just

been announced by Continental Carbon, Inc., of Cleveland, Ohio. The kit contains 25 one -watt carbon type resistors, a novel resistor paralleling chart, an RMA color code

selector, and a resistor replacement guide . . . which makes it pretty complete.

The resistor paralleling chart is an in- genious diagram that allows standard resistors provided in the kit to be paralleled to form most any resistance values that may be needed for exact replacements.

The RMA color code selector is composed of three colored celluloid discs that may be revolved in position to indicate the color. combination and corresponding resistance value of any standard RMA color code marked resistor.

Included with each kit . we nearly forgot this . . is a card which entitles the purchaser of each kit to the new Con- tinental Replacement Resistor Guide, which will be available as soon as data is secured for the latest radio sets.

Photoelectric Equipment The American Photoelectric Corporation

of New York City have introduced some neat photoelectric equipment which has a whole list of uses.

First on the list. is a Photoelectric Relay, employing a standard photoelectric cell, a '71-A amplifier tube and a relay with a current -carrying capacity of 25 watts, non - inductive load. The equipment is in a self- contained unit, and is designed to operate directly from an a -c. or d -c. 110 -volt light

The A.P.C. Photoelectric Relay

The A.P.C. Photoelectric Counter

supply, or from batteries. In operation the unit consumes less current than a 40 -watt lamp.

On the side of the case is a special adjusting screw whereby the unit may be set to operate at any desired light value. The, relay may be had in either the normally open - circuit or normally closed-circuit types, as desired.

Second on the list is the A.P.C. Photo -

The A.P.C. Projector

electric Counter, which is the same in all respects to the Photoelectric Relay just described except that it is equipped with a four -digit (0-9,999) counter which is coupled to the relay, and will count passing objects at any rate up to 360 per minute.

And last but not least is the A.P.C. Type A Projector designed to meet the need for a small, compact light source for energizing photoelectric cells. This projector was designed particularly for use with the Relay and the Counter previously described, and the center of the light beam is at the correct height (61/4 inches from the base) to strike the photocell of either of these instruments without further adjustment.

The projector uses a 32-c.p. automobile lamp and under normal conditions will throw a sufficiently powerful beam to operate the Relay over a distance of 30 feet and the Counter over a distance of 20 feet.

The projector is equipped with a polished metal reflector and with a ground and polished lens which is adjustable to permit sharp focusing of the light at any distance. When desired, filter holders and infra -red filters can be supplied for this projector so that the light beam will be invisible.

The Type A Projector can be supplied for

use on the following voltages: 110-120 volts a -c.; 110-120 volts d -c.; 6 volts battery supply.

ER -52 Tube The Everéady Raytheon Tube Division of

the National Carbon Company has announced the new ER -52 Dual Purpose Power Output Tube. This tube has been designed for use as a Class B amplifier in auto radio receivers or as a Class A amplifier in 110 - volt d -c. receivers.

The widely different characteristics required for these two types of service are obtained by employing two separate grids which are connected to separate base prongs. When used as a Class B amplifier in auto radio sets, the inner and outer grids are connected together and used as a control grid, thereby making the tube a high -mu triode. When used as a Class A amplifier in 110 -volt d -c. receivers, the inner grid is used as the control grid and the outer grid is connected to the plate, thereby providing a low -mu triode.

The characteristics of the tube are as follows:

Fil. Voltage 6.3 Fil. Current 0.3 Base 5 prong

CLASS B AMPLIFIER Plate Voltage 180 max. Grid Bias (both grids) 0 Plate Current* (2 tubes) 3.0 ma.

*At zero signal CLASS A AMPLIFIER

Plate and Outer Grid Volts 100 (120 max.)

Grid Bias (inner grid) 0 Plate Current 42 ma.

Increased output may be obtained by the use of two ER -52 tubes connected in push- pull, with zero bias. In this case either an 85 or 171-A may be used as a driver, with preference towards the latter.

216 SERVICE FOR

A/,

A_ c AssaTEIDfflä

APASS CONDENSERS,

TRUTEST Assorted By -Pass Condensers

A very handy assortment for the Ser- vice Man. Contains 12 of the most popular capacities in drawn metal cans; assorted as follows:

No. Cep'y Mfd. .I .25

2 .5 2 1.

.I

.25

.5

.5 I .

9D3289- Your Cost

s0 Cg JC

cutenr

Voltages 200 200 200 200 300 300 300 300 400 900

$3.25

REMARKABLE VALUES ON REPLACEMENT

PARTS !

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Index oF Monthly Literature AUTO -RADIO

Auto Radio Design and Installation, Part 2

M. J. Sheedy, Radio News, pp 155, September, 1932

Tubes 85 and 69 Duo -Diodes, and BR Rectifier L. Martin, Radio -Craft, pp 142, September, 1932

BROADCAST RECEIVERS

Amplifiers, A -F.

Application of Class B Audio L. E. Barton, Proc. I.R.E., pp, 1,085, July, 1932

Automatic Tone Control Electronics, pp 218, July, 1932

Class B Audio for Battery Receivers C. B. DeSoto, QST, pp 29, August, 1932

46, Class B Apparatus C. H. W. Nason, Radio -Craft, pp 151, September, 1932

Power Tube Chart and Impedance - Matching Data

Capt. P. V. O'Rourke, Radio World, pp 6, July 16, 1932

Recent Trends in Receiving Tube Design (56, 57, 58, 46, 82) Warner, Ritter and Schmit, Proc. 1.R.E., pp 1,247, August, 1932

Triple -Twin Tubes C. F. Stromeyer, Proc. I.R.E., pp. 1,149, July, 1932

Amplifiers, R -F.

Automatic Muting Systems Electronics, pp 218, July, 1932

Automatic Volume Control Systems W. S. Williams, Radio -Craft, pp 155, September, 1932

Lock -In Systems* Electronics, pp 219, July, 1932

Recent Trends in Receiving Tube Design (56, 57, 58, 46, 82) Warner, Ritter and Schmit, Proc. 1.R.E., pp 1,247, August, 1932

Receivers

Lincoln DeLuxe SW -33, Part 1

W. C. Dorf, Radio News, pp 148, September, 1932

Scott Allwave DeLuxe, Part 2

S. G. Taylor, Radio News, pp 160, September, 1932

Silver -Marshall 728SW McMurdo Silver, Radio News, pp 153, September, 1932 ibid, Short Wave Craft, pp 227, August, 1932

PUBLIC-ADDRESS SYSTEMS

Class A Prime P -A. Amplifier R. P. Glover, Modern Radio, pp 6, August, 1932

46, Class B Apparatus C. H. W. Nason, Radio -Craft, pp 151, September, 1932

Dynamic Microphone: Construction Zolnier and Selliken, Radio News, pp 150, September, 1932

Power Tube Chart and Impedance - Matching Data Capt. P. V. O'Rourke, Radio World, pp 6, July 16, 1932

Triple -Twin P -A. Amplifier H. Georges, Radio -Craft, pp 150, September, 1932


SHORT WAVE Hammarlund Comet "Pro" G. Fraser, Radio News, pp 156, September, 1932

Lincoln DeLuxe SW -33, Part 1

W. C. Dorf, Radio News, pp 148, September, 1932

Noise -Reducing Aerials* A. H. Lynch, Short Wave Craft, pp 212, August, 1932 ibid, Radio -Craft, pp 164, Septem- ber, 1932

Scott Allwave DeLuxe, Part 2

S. G. Taylor, Radio News, pp 160, September, 1932

Silver -Marshall 728SW McMurdo Silver, Short Wave Craft, pp 227, August, 1932 ibid, Radio News, pp 153, September, 1932

TESTING SYSTEMS

A.C.-D.C. Set Analyzer Multimeter T. J. Goldman, Radio News, pp 158, September, 1932

A.C.-D.C. Vacuum Tube Voltmeter J. E. Anderson, Radio World, pp 16, July 16, 1932

A.C. Voltages with D.C. Meter B. Thompson, Radio World, pp 5, July 30, 1932

Direct -Reading Short Circuit Tests for Vacuum Tubes A. G. Richardson, Electronics, pp 233, July, 1932

Dynatron Oscillator, A.C. K. Sloan, Radio News, pp 167, September, 1932

Improved Ohmmeter Modern Radio, pp 4, August, 1932

Universal Analyzer Radio -Craft, pp 138, September, 1932

TUBES

Power Tube Chart and Impedance - Matching Data Capt. P. V. O'Rourke, Radio World, pp 6, July 16, 1932

RCA 868 Phototube J. van Lienden, Radio News, pp 152, September, 1932

Recent Trends in Receiving Tube Design (56, 57, 58, 46, 82) Warner, Ritter and Schmit, Proc. I.R.E., pp 1,247, August, 1932


Tubes 55, ER -49, BR, 43, 29, 69, TS -257 L. Martin, Radio -Craft, pp 142, September, 1932

All articles listed on this page are cross-indexed for your convenience. Titles given are not necessarily the titles of the original articles, but in each case serve to determine the substance of the article. Listings marked with an asterisk (*) are abstracted in this issue. The material in each issue of SERVICE is alphabetically indexed on the Contents Page.

218 SERVICE

I(Î1)c Service helps.. ....

Sr SAYS

ICAN'T say I blame some Service Men for having installation fright" when they tackle auto radio jobs. There has

been too much "theoretical" and "technical" literature floating around which would give most anyone the idea that an auto radio job was in the same class as a telephone switch- board installation.

There are, of course, a few simple rules that must be followed if the job is to be a good one. For example, you've got to use a suppressor resistor on each spark plug, and one on the distributor. It is also vital that these suppressor resistors be capable of withstand- ing the heat from the motor and the high- tension current. If just one resistor breaks down under the strain it will cease to "suppress" and turn itself into a crackerjack noise- maker.

Now, believe it or not, the suppressors may be sufficient to reduce noise to the point where it is not noticeable in the receiver. However, a few 1.0-mfd. fixed condensers may have to be tucked in here and there to reduce sparking and surges. Like this: One from the "high" side of the ignition coil to ground; another across the interrupter contacts; a third across the generator brushes.

After all, the noise problem should be tackled with common sense-not theory. Which brings me to leads. They should be shielded for exactly the same reason we shield radio receivers ... except that in one case we do it to "keep the noise out" and in the other case to "keep the noise in." Again for the same reason, the leads should be as short as possible, and the shielding should be bonded directly to the chassis of the receiver. This shielding should continue right up to the point of the lead contact.

What else? Connections! Like the Ches- terfield Cigarette advertisements say, "They've got to be good." One poor connection may cause as much trouble as an "unsuppressed" spark plug, and keep you sweating around on the nastiest noise -hunting expedition you ever had. Make all connections "super -connections" in the first place, and you will end with a good job with no kinks to be ironed out.

The IRC people have a swell pamphlet on the subject, if you want one. No cost.

e4-wc_-eh, eia

The Newest Method of Servicing The measurement of resistance is fast becoming the recognized method of analyzing troubles in receivers.

Have you art,ohmmeter which will measure the resistance between different points in a radio set? We will show you how you can easily build an economical ohmmeter from any 0-1 milliammeter which you may have or can purchase for a few dollars. This ohmmeter can have any number of desired ranges to encompass all resistance values in present day sets.

IRC precision wound resistors are available in numerous values and have a high degree of accuracy so that in spite of the low cost, this ohmmeter will be com- parable in efficiency with the manufactured instruments.

By using a plug-in cable or prods which will reach the different points in a receiver, you can apply this ohmmeter for point-to-point resistance measurement.

If you do not have an ohmmeter, we will show you how to make one. If you have an ohmmeter, we will show you how to extend its range by using the accurately calibrated, precision wound IRC resistors.

Write us for complete information. We will send you FREE, full construc- tional details AND an ohmmeter scale which you can use on Weston and Jewell 0-1 milliammeters.

MOTOR RADIO SUPPRESSORS must withstand severe mechanical shock and vibration; he unaffected by temperature and moisture and be able to suppress ultra short waves generated by the spark. IRC MOTOR RADIO SUPPRESSORS are suitable for most makes of cars. They are moisture-proof- shock-proof-fire-proof and heat resistant. They have low capacity-positive contact-long life.

Send for Free Folder on Information on the Suppression of Motor Radio Noises. This folder is also enclosed in every kit of IRC Motor Radio Suppres- sors.

They're better beet:lose they're

Resistors for Replacements

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